public async void CreateInGenreRelationship_Test()
        {
            // Arrange
            var newBook = CreateBook();
            await _bookRepository.AddOrUpdateAsync(newBook);

            var newGenre = CreateGenre();
            await _genreRepository.AddOrUpdateGenreAsync(newGenre);

            var inGenre = new Relationships.InGenre();

            // Act
            await _genreRepository.CreateInGenreRelationshipAsync(newGenre, newBook, inGenre);

            var returnedBook = (await _genreRepository.GetInGenreBookRelationshipAsync(newGenre, inGenre))
                               .ToList().FirstOrDefault();

            // Assert
            Assert.True(newBook.Title == returnedBook.Title);

            // Clean up
            await _genreRepository.DeleteInGenreRelationshipAsync(newGenre, newBook, inGenre);

            await _bookRepository.DeleteBookAsync(newBook);

            await _genreRepository.DeleteGenreAsync(newGenre);
        }
        public async Task <IActionResult> AddUpdateBookAsync(Book book)
        {
            await _bookRepository.AddOrUpdateAsync(book);

            foreach (var genre in book.Genres)
            {
                await _genreRepository.CreateInGenreRelationshipAsync(genre, book, new Relationships.InGenre());
            }

            return(Ok());
        }