// ham update
        public void update(string maloai, string tenloai)
        {
            LoaiBanh loaiBanh = db.LoaiBanhs.Single(p => p.MaLoaiBanh == maloai);

            loaiBanh.TenLoaiBanh = tenloai;
            db.SubmitChanges();
        }
        // ham xoa loai banh
        public void delete(string maloai)
        {
            LoaiBanh loaiBanh = db.LoaiBanhs.Single(p => p.MaLoaiBanh == maloai);

            db.LoaiBanhs.DeleteOnSubmit(loaiBanh);
            db.SubmitChanges();
        }
        // ham them loai banh
        public void insert(string tenloai)
        {
            LoaiBanh loaiBanh = new LoaiBanh();

            loaiBanh.MaLoaiBanh  = laymabanh();
            loaiBanh.TenLoaiBanh = tenloai;
            db.LoaiBanhs.InsertOnSubmit(loaiBanh);
            db.SubmitChanges();
        }