public void AddUserToScheduleItem(ScheduleItemAddress scheduleItemAddress, Guid userID)
        {
            var scheduleItem = GetScheduleItem(scheduleItemAddress);

            repository.AddUserRelationship(scheduleItem.ToScheduleItemSmall(), userID);

            //cache.InvalidateItem(scheduleItem);
            //var key = string.Format("GetScheduleItemsByUser-UserID:{0}", userID);
            //cache.InvalidateContains(key, StringComparer.InvariantCultureIgnoreCase);
        }