public async Task <IActionResult> AddBookAsync(string isbn) { Book book = await BookService.AddByISBNAsync(isbn); if (book == null) { return(HttpBadRequest("the provided ISBN does not resolve to a book in our backend service")); } var resource = await BookAssembler.ConvertToResourceAsync(book); return(CreatedAtRoute("api", new { id = book.Id }, resource)); }