How about using an IValidator instead? http://www.david-tec.com/2012/06/EPiServer-7-Preview---IValidator-interface/

Hi,

I also think that Per's idea of implementing validation using IValidate<T> is interesting.

When you use HttpContext.Current to resolve validated page url it will work only when saving/publishing in the web browser. If you try to save the page programmatically, for example in the Scheduled Job, then the Current context could be not relevant.

The IValidate could be used with any type. It could be used with a property or a with a whole Content. When you use it on the property level, like IValidate<XhtmlString> then you will get same effect as using ValidationAttribute. But you will not have access to validated page (and it will validate all XHtml strings in your system).

To get access to the content you could implement IValidate<YourPageModel>.  Then in the Validate method you will validate the specific property (like the Xhtml property). Using UrlResolver you will be able to get page URL

public class MessageValidator : IValidate<ArticlePage>
{
    IEnumerable<ValidationError> Validate(ArticlePage instance)
    {      
        if (instance.Message.Length > 100)
        {
// get URL to the page
ServiceLocator.Current.GetInstance<UrlResolver>().GetUrl(instance.PageLink);


            return new[] { new ValidationError() {
                ErrorMessage = "Max length is 100",
                PropertyName = "Message",
                Severity = ValidationErrorSeverity.Error,
                ValidationType = ValidationErrorType.AttributeMatched
            } };
        }
 
        return Enumerable.Empty<ValidationError>();
    }
}

IValidate is working pretty well.
The only drawback is that I can't use it as an attribute on a property but that isn't really necessary in this case.

Thanks, both of you.

For property level validation I would look for either built-in Data Annotation validation or some custom if needed.