GetBook.cs

  [HttpGet("{id}")]
        public async Task<ActionResult<BookInfoDto>> GetBook(int id)
        {
            BookInfoDto book = await _db.Books
            .Select(x => new BookInfoDto() { BookID = x.BookID, Name = x.Name, AuthorName = x.Author.Name })
            .SingleOrDefaultAsync(x => x.BookID == id);

            if (book == null)
                return NotFound("İstenilen kitap bulunamadı");
            return Ok(book);
        }