DataAnnotations attributes on custom control - asp.net-mvc-4

Question

I've used a custom control (HTML Helper) to build an Autocomplete controller.
it works great, the only thing is the validation problem.
on the client side, the validation works fine when jquery.validation.js is out of the picture, (for empty text box it gives an error message).
if the user selects something from the autocomplete, so im fine.
but when the user input is just junk, then the HttpPost needs to handle the junk & return an error message to the user.
HOW??
also, i've seen a DataAnnotation called Remote, which can manage the validation on the client side, is it better ? if so, how can i add DataAnnotaion on a custom control ??
Thank's :)
here is my code:
Index.cshtml
#using (Html.BeginForm("Index", "Create"))
{
#Html.AutocompleteFor(Url.Action("AutoCompleteServiceProviders", "Create"), true, "ex. Shower", c => c.service_id, a => a.name)
<input type="submit" id="search" value="" />
}
AutoComplete.cs
private static MvcHtmlString CreateAutocomplete<TModel>(this HtmlHelper<TModel> helper, string actionUrl, bool? isRequired, string placeholder, params Expression<Func<TModel, object>>[] expression)
{
var builder = new StringBuilder();
foreach (var item in expression)
{
var attributes = new Dictionary<string, object>
{
{ "data-autocomplete", true },
{ "data-action", actionUrl }
};
if (!string.IsNullOrWhiteSpace(placeholder))
{
attributes.Add("placeholder", placeholder);
}
if (isRequired.HasValue && isRequired.Value)
{
attributes.Add("required", "required");
}
Func<TModel, object> method = item.Compile();
var value = (Object)null;
if ((TModel)helper.ViewData.Model != null)
{
value = method((TModel)helper.ViewData.Model);
}
var baseProperty = (string)null;
var hidden = (MvcHtmlString)null;
if (item.Body is MemberExpression)
{
baseProperty = ((MemberExpression)item.Body).Member.Name;
hidden = helper.Hidden(baseProperty, value);
attributes.Add("data-value-name", baseProperty);
}
else
{
var op = ((UnaryExpression)item.Body).Operand;
baseProperty = ((MemberExpression)op).Member.Name;
hidden = helper.Hidden(baseProperty, value);
}
attributes.Add("data-value-id", "service_id");
var automcompleteName = baseProperty + "_autocomplete";
var textBox = (MvcHtmlString)null;
if (value != null)
{
textBox = helper.TextBox(automcompleteName, value, string.Empty, attributes);
}
else
{
textBox = helper.TextBox(automcompleteName, null, string.Empty, attributes);
}
builder.AppendLine(hidden.ToHtmlString());
if (baseProperty == "name")
{
builder.AppendLine(textBox.ToHtmlString());
}
}
return new MvcHtmlString(builder.ToString());
}

Answer 1

You can get your validation from here:
var validation = htmlHelper.ValidationMessageFor(expression, null, new Dictionary<string, object>());
UPDATE:
I use TagBuilder to create tags. What I do with tagbuilder is add that validation to a span or div tag and let the unobtrusive javascript hide/show it when needed. It returns an MVCHtmlString you can just append it to the element you want to display it in