public ActionResult Register(RegisterInSessionViewModel vm)
        {
            var user = _userService.CurrentUser;
            var session = _sessionService.GetById(vm.SessionId);

            _sessionService.Register(user.Id, vm.SessionId);

            return new EmptyResult().WithSuccessMessage(string.Format("You have been successfully registered in session: {0}", session.Title));
        }
        public ActionResult Register(int id)
        {
            // check if user already registered
            var session = _sessionService.GetById(id);
            var user = _userService.CurrentUser;

            if (session == null)
                return new EmptyResult().WithErrorMessage(string.Format("Could not find session by Id: {0}", id));

            var vm = new RegisterInSessionViewModel
            {
                // check permissions
                SessionId = session.Id,
                IsRegistered = session.Users.Any(u=>u.UserId == user.Id),
                SessionDescription = new SessionViewModel
                {
                    Id = session.Id,
                    Overview = session.Overview,
                    End = session.End,
                    RegistrationCloseAt = session.RegistrationClosedAt,
                    Start = session.Start,
                    Title = session.Title,
                    TypeId = (int)session.Type,
                    Address = session.City
                }

            };

            return PartialView("_Register", vm);
        }