Getting full property name using ModelMetadata

Question

I'm trying to create an HtmlHelper that will create Bootstrap-compatible form fields. My first goal was to create an HtmlHelper that will create the surrounding div:

<div class="control-group"> ... </div>

Following the excellent advice here and also here I managed to get it to work relatively quickly. But it doesn't always work.

I have a ViewModel with a complex property, so in my form I access the field m=>m.Complex.Element . In my helper I check the element for validation errors. I use ModelMetadata.FromLambdaExpression(expression, html.ViewData) . The metadata I get back has the property name Element, and not Complex.Element.

When I check the ModelState for this property, I can't find it, because the ModelState keeps the full name - Complex.Element.

I can look for partial matches, hoping there's no other Element, but that seems like a nasty bug waiting to happen. How can I get the full property name from the expression?

Answer 1

It's a good thing the MVC sources are out in the open. The proper way to get the ModelState property name is by using

var propertyName = ExpressionHelper.GetExpressionText(expression);

Answer 2

I've used the following to get it for the current model before, you may have to append the property name to this to get it for the property though.

ViewContext.ViewData.TemplateInfo.HtmlFieldPrefix;

Otherwise pull out reflector/ilspy/whatever and check what your EditorFor/TextBoxFor or whatever method is rendering your editor does.

Answer 3

I've used a combination of both answers for an attribute I needed. Together, both of these answers provide a working attribute I can use in both views and nested editor templates. Here's my example:

public static MvcHtmlString HasErrorClassFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, TProperty>> expression)
{
    string expressionText = ExpressionHelper.GetExpressionText(expression);

    string htmlFieldPrefix = htmlHelper.ViewData.TemplateInfo.HtmlFieldPrefix;

    string fullyQualifiedName;

    if (htmlFieldPrefix.Length > 0)
    {
        fullyQualifiedName = string.Join(".", htmlFieldPrefix, expressionText);
    }
    else
    {
        fullyQualifiedName = expressionText;
    }

    bool isValid = htmlHelper.ViewData.ModelState.IsValidField(fullyQualifiedName);

    if (!isValid)
    {
        return MvcHtmlString.Create("has-error");
    }

    return MvcHtmlString.Empty;
}