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...

2 Answers 2


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.

public interface MyI{

   string DoWork{get;}

public class MyC : MyI {

  public string DoWork => "Hello world";

var result = service.GetItem<MyI>("/mypath", InferType:true)
  • Good alternative. I thought something like that would work as well, but didn't have time to research it first. Dec 6, 2017 at 9:39
  • @Michael - This is actually still not working for me unfortunately when the classes are split with a partial
    – Nona Drake
    May 18, 2018 at 20:58

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();

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