public int CreateArtist(CreateArtistRequest request) { Require.NotNull(request, nameof(request)); if (_musicRepository.GetArtists(artist => artist.Name.Equals(request.Name)).SingleOrDefault() != null) { throw new AccountAlreadyExistsException("Artist with such name already exists"); } var newArtist = new Artist( request.Name, request.Description); var artistId = _musicRepository.CreateArtist(newArtist); return(artistId); }