public bool InsertTheLoai(int id, string ten)
        {
            string query = string.Format("INSERT INTO dbo.[TheLoai](MaTheLoai, TenTheLoai)" +
                                        "VALUES('{0}', N{1})", id, ten);
        }

        public bool InsertTheLoai(TheLoai tl)
        {
            string query = string.Format("INSERT INTO dbo.[TheLoai](MaTheLoai, TenTheLoai)" +
                                        "VALUES('{0}', N{1})", tl.MaTheLoai, tl.TenTheLoai);
        }