Question

I have a Regular Expression Validation for a Single Capital Letter, but it does not work.
When I put in a valid letter, I get the error message;

        [DisplayName("Contract Letter")]
        [RegularExpression("[A-Z]", ErrorMessage = "Must be a letter")]
        [Required(ErrorMessage = "A Letter is required")]
        public string ContractNo_Letter { get; set; }

I am only allowing the input of 1 letter.

Answer 1

A couple of things to consider here:

• The regular expression you have specified will evaluate to true provided that there is at least one letter from A-Z anywhere within the expression. For example: 8979*(&#$HJ will evaluate to true. To match exactly one letter, you can wrap your regex with the special characters: ^ (start of line), and $ (end of string).
• Regular expressions in DataAnnotations are case-sensitive. To check both upper and lower-case letters, use [A-Za-z].

So, to match a single letter without case sensitivity, use ^[A-Za-z]$.