public void AddAuthor(AuthorModel author) { _validator.ValidateAuthor(author); var authorFilter = new AuthorFilterModel { Name = author.Name }; var dbAuthor = _authorRepository.Get(authorFilter).FirstOrDefault(); if (dbAuthor is not null) { throw new CustomApiException(HttpStatusCode.UnprocessableEntity, Constants.AUTHORALREADYEXISTSERROR); } dbAuthor = _mapper.Map <AuthorEntity>(author); _authorRepository.Insert(dbAuthor); }