Why doesn't the regular expression below work?

Question

I'm using data annotation for validation but code below does not work:

    [RegularExpression(@"^[0-9]+$", ErrorMessage = "Only Numbers allowed!")]
    [Required(ErrorMessage = "Client Id Required")]
    [Display(Name="Client ID")]
    public int ClientId
    {
       ...}

Answer 1

Try this instead:

[RegularExpression(@"^\d+$", ErrorMessage = "Only numbers allowed")]

Answering your question "Why it's not working?", because The RegexValidator isn't called when the field is empty, you must use the RequiredFieldValidator in combination.