Question

I have a model like below:

public class CreateStockcheckJobModel
{
    [Engineer(true)]
    public EngineerModel Engineer { get; set; }
}

I’m rendering the Engineer property in a View<CreateStockcheckJobModel> using Html.EditorFor(m => m.Engineer, "EngineerEditor").

How do I access the value in the Engineer attribute (in this case true) from within the code in my partial view (EngineerEditor.ascx)?

---

Below is my editor code

<%@ Control Language="C#" Inherits="ViewUserControl<EngineerModel>" %>
<% if (PropertyImRenderingHasAttributeWithTrueBooleanValue) // What goes here?
   { %>
<p>Render one thing</p>
<% }
   else
   { %>
<p>Render another thing</p>
<% } %>

I’m aware of reflection, however i’m unsure how to use it as the attribute isn’t added to the EngineerModel class it’s added to the Engineer property of the CreateStockcheckJobModel class. If i could get the PropertyInfo that I’m rendering from the editor code then I’d be sorted, but I don’t know how to get that information. If I go down the route of enumerate all properties in the CreateStockcheckJobModel class then I’m going to get issues if I have more than one EngineerModel property (one might have the attribute with True, another might have False).

Answer 1

This could be done easily in ASP.NET MVC 3 and later by implementing the IMetadataAware interface on your custom EngineerAttribute:

public class EngineerAttribute : Attribute, IMetadataAware
{
    public EngineerAttribute(bool isFoo)
    {
        IsFoo = isFoo;
    }

    public bool IsFoo { get; private set; }

    public void OnMetadataCreated(ModelMetadata metadata)
    {
        metadata.AdditionalValues["IsFoo"] = IsFoo;
    }
}

and then inside the template:

<%@ Control Language="C#" Inherits="ViewUserControl<EngineerModel>" %>
<%
    var isFoo = (bool)ViewData.ModelMetadata.AdditionalValues["IsFoo"];
%>
<% if (isFoo) { %>
    <p>Render one thing</p>
<% } else { %>
    <p>Render another thing</p>
<% } %>

Unfortunately this interface doesn’t exist in ASP.NET MVC 2. To achieve the same functionality you could write a custom metadata provider:

public class MyMetadataProvider : DataAnnotationsModelMetadataProvider
{
    protected override ModelMetadata CreateMetadata(
        IEnumerable<Attribute> attributes, 
        Type containerType, 
        Func<object> modelAccessor, 
        Type modelType, 
        string propertyName
    )
    {
        var metadata = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);
        var engineer = attributes.OfType<EngineerAttribute>().FirstOrDefault();
        if (engineer != null)
        {
            metadata.AdditionalValues["IsFoo"] = engineer.IsFoo;
        }
        return metadata;
    }
}

that you will register in your Application_Start in order to replace the default one:

ModelMetadataProviders.Current = new MyMetadataProvider();

And now you could access this metadata in your template the same way as I showed earlier, using ViewData.ModelMetadata.AdditionalValues["IsFoo"]. Obviously you could put an arbitrarily complex object inside the AdditionalValues property, not just booleans.

Also you might find the following article useful about metadata.