Backslash escaping in RegularExpressionValidator

Question

I need to ensure that the input value contains at least one dot, so i use the following:

<asp:RegularExpressionValidator runat="server" ControlToValidate="MyInput" Text="*" ErrorMessage="must contain at least one dot" ValidationExpression="\.+" />

And that doesn't work. By inspecting the page source i can see that ASP.NET escapes the backslash character so in java-script it looks like "\\.+". Why does it do so and how do i prevent RegularExpressionValidator from escaping it?

Answer 1

The double escape is necessary because the backslash is used for escape sequences in both JavaScript and regular expressions. A quick test to illustrate this point:

alert('42'.match("\d"));     // no match
alert('42'.match("\\d"));    // match

But that does not solve your problem. First step in troubeshooting: change the validation expression to a. Does it not fail on "foo" and pass on "bar"? If not, something else is wrong on your page - possibly an unrelated JavaScript bug causes the validation code to be skipped.

Slightly off topic: Your validation expressions can be trimmed to \. (without the plus), as you really only care about matching a single dot.

Answer 2

If you want to check if the input contains at least one dot, your expression is incorrect. It matches only input that consist only of dots.

You should use

.*\..*

If escaping proves to be a problem, too, use [.] instead of \..

Note that the RegularExpressionValidator does not validate empty fields. Use the RequiredFieldValidator to do this.