We have two different kinds of route at present, /Api/{AppId}/{Controller}/{Id} and /Api/{Controller}/{Id}. The Linked route provider ensures that if we PATCH or PUT to either of these that we also invalidate the cache for the same route without the {Id} parameter

Config

config.MessageHandlers.Add(new CachingHandler
 {
     UriTrimmer = (uri) => uri.LocalPath,
     LinkedRoutePatternProvider = LinkedRoutePatternProvider
 });

public static IEnumerable<string> LinkedRoutePatternProvider(string s, HttpMethod httpMethod)
{
  var appAware = new Regex("/Api/[0-9]+/([a-z]|[A-Z])+/[0-9]+");
  if (appAware.IsMatch(s))
  {
      var sections = s.Split('/');
      var appId = sections[2];
      var controller = sections[3];

      return new[] { string.Format("/Api/{0}/{1}", appId, controller) };
  }

  var normal = new Regex("/Api/([a-z]|[A-Z])+/[0-9]+");
  if (normal.IsMatch(s))
  {
      var sections = s.Split('/');
      var controller = sections[2];

      return new[] { string.Format("/Api/{0}", controller) };
  }

  return new string[] { };
}

Tests

[Subject("Linked route pattern provider")]
public class When_getting_linked_routes_for_a_context_specific_resource
{
    private static IEnumerable<string> result;

    private Because of = () => result = WebApiConfig.LinkedRoutePatternProvider("/Api/1/Forms/2", null);

    private It should_link_to_the_parent_collection = () => result.ShouldContain("/Api/1/Forms");
}

[Subject("Linked route pattern provider")]
public class When_getting_linked_routes_for_a_non_specific_resource
{
    private static IEnumerable<string> result;

    private Because of = () => result = WebApiConfig.LinkedRoutePatternProvider("/Api/Users/1", null);

    private It should_link_to_the_parent_collection = () => result.ShouldContain("/Api/Users");
}