ASP.NET Core: ShortName in the Display attribute (DataAnnotations)

Question

In an ASP .NET Core 1.1 project (VS 2017) I try to use the ShortName attrubute of the Display property in order to use the DisplayFor

Answer 1

To get the ShortName property using this method, you need to extract the Display attribute manually because it's not part of the default metadata. For example, something like this will work:

var defaultMetadata = m as 
    Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadata;
if(defaultMetadata != null)
{
    var displayAttribute = defaultMetadata.Attributes.Attributes
        .OfType()
        .FirstOrDefault();
    if(displayAttribute != null)
    {
        return displayAttribute.ShortName;
    }
}
return m.DisplayName;

To plug that into your helpers, I would abstract away the method slightly as there's some duplicate code in there, so you would end up with a private method like this:

private static IHtmlContent MetaDataFor(this IHtmlHelper html, 
    Expression> expression,
    Func property)
{
    if (html == null) throw new ArgumentNullException(nameof(html));
    if (expression == null) throw new ArgumentNullException(nameof(expression));

    var modelExplorer = ExpressionMetadataProvider.FromLambdaExpression(expression, html.ViewData, html.MetadataProvider);
    if (modelExplorer == null) throw new InvalidOperationException($"Failed to get model explorer for {ExpressionHelper.GetExpressionText(expression)}");
    return new HtmlString(property(modelExplorer.Metadata));
}

And your two public methods like this:

public static IHtmlContent DescriptionFor(this IHtmlHelper html, Expression> expression)
{
    return html.MetaDataFor(expression, m => m.Description);
}

public static IHtmlContent ShortNameFor(this IHtmlHelper html, 
    Expression> expression)
{
    return html.MetaDataFor(expression, m => 
    {
        var defaultMetadata = m as 
            Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultModelMetadata;
        if(defaultMetadata != null)
        {
            var displayAttribute = defaultMetadata.Attributes.Attributes
                .OfType()
                .FirstOrDefault();
            if(displayAttribute != null)
            {
                return displayAttribute.ShortName;
            }
        }
        //Return a default value if the property doesn't have a DisplayAttribute
        return m.DisplayName;
    });
}