public PartialViewResult ParticipantList(ParticipantListViewModel vm)
        {
            var @event = db.Events.Find(vm.EventId);
            eventService.AddParticipantToEvent(@event.EventId, vm.AddedUserId);

            vm.EventParticipants = @event.EventParticipants.ToList();
            vm.AvailableUsers = eventService.GetAvailableUsersForEvent(vm.EventId);

            return PartialView(vm);
        }
        public PartialViewResult ParticipantList(int eventId)
        {
            var @event = db.Events.Find(eventId);
            ParticipantListViewModel vm = new ParticipantListViewModel()
            {
                EventId = eventId,
                EventParticipants = @event.EventParticipants.ToList(),
                AvailableUsers = eventService.GetAvailableUsersForEvent(eventId)
            };

            return PartialView(vm);
        }