public IEnumerable <string> getListTheLoaistring()
        {
            IEnumerable <TheLoai> listTheLoai       = BaiDangSUM.getTheLoai();
            List <string>         listTheLoaistring = new List <string>();

            foreach (TheLoai tg in listTheLoai)
            {
                listTheLoaistring.Add(tg.tenloaisach);
            }

            return(listTheLoaistring.AsEnumerable());
        }
        public IEnumerable <TheLoai> getListTheLoai()
        {
            IEnumerable <TheLoai> listTG = BaiDangSUM.getTheLoai();

            return(listTG);
        }