public BLGiaoVien() { quanLyTruongHoc = new QuanLyTruongHocDataContext(); }
public BLLop() { quanLyTruongHoc = new QuanLyTruongHocDataContext(); }
public BLHocSinh() { quanLyTruongHoc = new QuanLyTruongHocDataContext(); }