EmailAddressAttribute without being required

Question

I have a [EmailAddress] DataAnnotation from .net 4.5 on a model property, which returns a 'The Email field is not a valid e-mail address.' error during validation, when the Email property is empty.

While this is technically true, I would have expected this empty value to only be caught with a [Required] annotation.

Is there any parameter I'm missing which can be passed to the [EmailAddress] annotation to allow empty strings to validate, or do I have to fall back to using a custom validator regular expression?

Answer 1

There is no such parameter for EmailAddressAttribute. The validation code for this attibute is following:

if (value == null)
{
    return true;
}
string input = value as string;
return ((input != null) && (_regex.Match(input).Length > 0));

And the regex is defined as (there will be no match for empty string):

_regex = new Regex(@"^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$", RegexOptions.Compiled | RegexOptions.ExplicitCapture | RegexOptions.IgnoreCase);

To achieve your goal you can create your can inherit from DataTypeAttribute override IsValid method, so it will return true for empty or null strings and use instance of EmailAddressAttribute. This should be something like this:

public override bool IsValid(object value)
{
    if (value == null)
    {
        return true;
    }
    string input = value as string;
    var emailAddressAttribute = new EmailAddressAttribute();

    return (input != null) && (string.IsNullOrEmpty(input) || emailAddressAttribute.IsValid(input));
}