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);
}