public void deleteAttend(int bookId, int authorId)
        {
            ThamGia e = db.ThamGias.SingleOrDefault(x => x.MaSach == bookId && x.MaTacGia == authorId);

            db.ThamGias.Remove(e);
            db.SaveChanges();
        }
 public void createAttend(ThamGia e)
 {
     db.ThamGias.Add(e);
     db.SaveChanges();
 }