How can I set a RegularExpression data annotation's regular expression argument at runtime?

Question

We manage several ASP.NET MVC client web sites, which all use a data annotation like the following to validate customer email addresses (I haven\'t included the regex here,

Answer 1

The easiest way is to write a custom ValidationAttribute that inherits from RegularExpressionAttribute, so something like:

public class EmailAttribute : RegularExpressionAttribute
    {
        public EmailAttribute()
            : base(GetRegex())
        { }

        private static string GetRegex()
        {
            // TODO: Go off and get your RegEx here
            return @"^[\w-]+(\.[\w-]+)*@([a-z0-9-]+(\.[a-z0-9-]+)*?\.[a-z]{2,6}|(\d{1,3}\.){3}\d{1,3})(:\d{4})?$";
        }
    }

That way, you still maintain use of the built in Regex validation but you can customise it. You'd just simply use it like:

[Email(ErrorMessage = "Please use a valid email address")]

Lastly, to get to client side validation to work, you would simply add the following in your Application_Start method within Global.asax, to tell MVC to use the normal regular expression validation for this validator:

DataAnnotationsModelValidatorProvider.RegisterAdapter(typeof(EmailAttribute), typeof(RegularExpressionAttributeAdapter));