public async Task <Unit> Handle(AddAnnouncementCommand request, CancellationToken cancellationToken) { if (_announcementRepository.CountAllByDate(request.PublicationDate, request.UserId).Result >= 5) { throw new ArgumentException("The number of the same publication date cannot be over than 5."); } var announcement = new Domain.Announcement(request.Id, request.Title, request.Content, request.PublicationDate, request.UserId); await _announcementRepository.AddAsync(announcement); await _announcementRepository.SaveChangesAsync(); return(Unit.Value); }