public ActionResult Update(int projectId, int activityId, ActivityViewModel.Input model)
        {
            var activity = DbSession.Load<Activity>(activityId);
            if (activity == null || activity.Project.ToIdentifier() == projectId)
                HttpNotFound();
            model.Dependencies = model.Dependencies ?? new List<int>();
            activity.Update(model.MapTo<Activity>(), DbSession);
            var data = activity.MapTo<ActivityViewModel>();

            data.Project = DbSession.Load<Project>(model.Project).MapTo<EntityViewModel>();
            return new JsonNetResult {Data = data};
        }