ModelMetadata additional attributes is always empty

Question

I am trying to access a model's metadata attributes to create a helper to automatically add HtmlAttributes based on DataAnnotations.

Problem is, the attributes are always empty.

I have 2 basic classes to try on an empty project:

namespace MegaInterestingProject
{
    public class HomeController : Controller
    {
        public string Index()
        {
            var model = ModelMetadata.FromLambdaExpression<HomeModel, string>(x => x.User, new ViewDataDictionary<HomeModel>());

            return model.Description;
        }
    }

    public class HomeModel
    {
        [Required]
        [MaxLength(13)]
        [MinLength(11)]
        [DisplayName("displayname")]
        [Description("description")]
        public string User { get; set; }
    }
}

Here model.Description is always empty and the AdditionalValues dictionary is always empty.

Maybe something is missing here?

Here is a reference project I added on GitHub: https://github.com/erickgirard/TestHtmlAttributesHelper

Answer 1

Your using the wrong attribute for generating the ModelMetadata . You need to use the DisplayAttribute in System.ComponentModel.DataAnnotations (not DisplayNameAttribute in System.ComponentModel .

public class HomeModel
{
  [Display(Name = "displayname", Description = "description")]
  public string User { get; set; }
}

Answer 2

You did not place the attribute on the model, but on a property of a model.

A custom helper function that accesses the metadata of a property within a model would look like this:

public static MvcHtmlString CustomHelperFunctionFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
{
    var propertyName = ExpressionHelper.GetExpressionText(expression);
    var metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
    var displayname = metadata.DisplayName;
    var description = metadata.Description;

    return new MvcHtmlString("have fun!");
}