Adding Custom (non sitecore field) property or method to Glass Mapper Class Returns Null

Question

I've got an issue with extending the partial class from a TDS generated Template for glass mapper. Basically, I want to add a method to the underlying class to say have a custom string based on a property value.

public partial class _Contributor {
   public virtual string ContributorUrlQueryString => $"?name={HttpUtility.UrlEncode(ContributorName)}&id={Id}".ToLower();
}

var contributor = _contentRepository.GetContentItem(id);

Glass Mapper - 1 never hits the function and 2 returns null. Am I missing something?

Update: Changing calling code to use concrete class instead of Interface allows the code to be hit and the expected results: var contributor = _contentRepository.GetContentItem<_Contributor>(id);

However, I would still like to use the Interface...

Answer 1

Soren's answer is correct.

Another way to solve this would be to used inferred types and infer from your interface to the concrete type, this assumes there is a one-to-one mapping for templates and classes.

[SitecoreType]
public interface MyI{

   string DoWork{get;}
}

[SitecoreType(TemplateId='00000')]
public class MyC : MyI {

  public string DoWork => "Hello world";
}

var result = service.GetItem<MyI>("/mypath", InferType:true)

Answer 2

If you are using Glass Mapper to map an item to an interface it will create a proxy class implementing that interface, but it will have no connection to the concrete class (or any other implementation of that interface).

If you use it to map to a concrete class it will still create a proxy but it will pass the call on to the actual implementation (for virtual methods/properties, non-virtual will always call the actual class).

However, I would still like to use the Interface...

Well, one option would then be to make an extension method, like this:

public static class Extensions
{
    public static string ContributorUrlQueryString(this IContributor contributor)
    {
        return $"?name={HttpUtility.UrlEncode(contributor.ContributorName)}&id={contributor.Id}".ToLower();
    } 
}