Validation helper

gistfile1.cs

public static class Extensions
{
	public static MvcHtmlString WriteIfError<M, P>(this HtmlHelper<M> htmlHelper, Expression<Func<M, P>> expression, string value)
	{
		string expressionText = ExpressionHelper.GetExpressionText(expression);

		string modelName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(expressionText);

		if (!htmlHelper.ViewData.ModelState.ContainsKey(modelName))
		{
			return null;
		}

		ModelState modelState = htmlHelper.ViewData.ModelState[modelName];
		ModelErrorCollection modelErrors = (modelState == null) ? null : modelState.Errors;
		ModelError modelError = (((modelErrors == null) || (modelErrors.Count == 0)) 
			? null 
			: modelErrors.FirstOrDefault(m => !String.IsNullOrEmpty(m.ErrorMessage)) ?? modelErrors[0]);

		if (modelError == null)
		{
			return null;
		}

		return MvcHtmlString.Create(value);
	}
}