Question

I use RegularExpressionAttribute on my EF meta data like so:

[RegularExpression("[A-Z]+")]
public string Code { get; set; }

And it correctly does not let me enter anything other than A-Z anywhere in the field.

Elsewhere I want to use the same reg expressions in code, so I turned to Regex like so:

var regex = new Regex("[A-Z]+");
Console.WriteLine(regex.IsMatch("B")); //true
Console.WriteLine(regex.IsMatch("1")); //false
Console.WriteLine(regex.IsMatch("A1")); //true - why?

Also RegexStringValidator works the same as Regex.

What am I doing wrong?

Answer 1

var regex = new Regex("[A-Z]+");
Console.WriteLine(regex.IsMatch("A1")); //true - why?

That regex says to match one or more upper case latin letters. And “A1” contains an upper case latin letter.

By default regexes match anywhere in the string. To match the whole string start with a “^” start of string anchor and end with a “$” end of string anchor:

 var regex = new Regex("^[A-Z]+$");
 Console.WriteLine(regex.IsMatch("A1")); 

will show false.

(There are a whole set of anchors in .NET regular expressions.)