In a view model I have the following regular expression attribute, but it does not work.
[RegularExpression(@"(?=[A-Z]+)(?=[a-z]+)(?=[0-9]+)", ErrorMessage = "Password must contain digits as well as lower and upper case letters.")]
So, the password string must contain at least one lower-case, one upper-case letter and at least one digit.
I looked at Regular Expressions: Is there an AND operator? but I could not make it work.
Any help is appreciated. Thanks.
First, you need .* inside your look-ahead clauses to enable those characters to be at any position in the matching string. Without that- all those characters would have to be at the start of your string.
Second, you need to actually have a capturing clause, or you'll get a null match- which will be considered invalid (Why? See below). So
(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])[A-Za-z0-9]*
would give you the entirety of the matching password. You could check password length here as well-
(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])[A-Za-z0-9]{8,}
Would make the password have to be greater than 8 characters in length.
As for why you need a value captured by the regex, the RegexValidationAttribute's IsValid(object value) method uses the following logical statement to return if the entered value is valid according to the regex. (where m is the Match from the given pattern on the given value, and stringValue is the given value)
return (m.Success && m.Index == 0 && m.Length == stringValue.Length);
Consider if you had the validating RegEx of .{3,8} - meaning any string between three and eight characters in length. You attempt to validate the value 123456789. The Regex Matches this string! 12345678 is between three and eight characters in length! Actually, so is 23456789. And 123, for that matter. Just checking for a match is not enough, you must further check that the whole value matches.
Use .* inside your lookaround to match your condition.
(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])
