How can I set a RegularExpression data annotation's regular expression argument at runtime?

Question

We manage several ASP.NET MVC client web sites, which all use a data annotation like the following to validate customer email addresses (I haven\'t included the regex here,

Answer 1

Do you really want to put the regex in database/config file, or do you just want to centralise them? If you just want to put the regex together, you can just define and use constants like

public class ValidationRegularExpressions {
    public const string Regex1 = "...";
    public const string Regex2 = "...";
}

Maybe you want to manage the regexes in external files, you can write a MSBuild task to do the replacement when you build for production.

If you REALLY want to change the validation regex at runtime, define your own ValidationAttribute, like

[RegexByKey("MyKey", ErrorMessage = "Email address is not valid")]
public string Email { get; set; }

It's just a piece of code to write:

public class RegexByKeyAttribute : ValidationAttribute {
    public RegexByKey(string key) {
        ...
    }

    // override some methods
    public override bool IsValid(object value) {
        ...
    }
}

Or even just:

public class RegexByKeyAttribute : RegularExpressionAttribute {
    public RegexByKey(string key) : base(LoadRegex(key)) { }

    // Be careful to cache the regex is this operation is expensive.
    private static string LoadRegex(string key) { ... }
}

Hope it's helpful: http://msdn.microsoft.com/en-us/library/cc668224.aspx