public async Task AddCalendar(long userId, CalendarViewModel calendarViewModel)
        {
            using (var tran = new TransactionScope(TransactionScopeAsyncFlowOption.Enabled))
            {
                var calendar = await calendarRepository.CreateAsync(new Calendar
                {
                    Group = calendarViewModel.Group,
                    Title = calendarViewModel.Title
                });

                await userRepository.AddCalendar(userId, calendar);

                tran.Complete();
            }
        }