void m_btn_them_mot_chuc_nang_Click(object sender, EventArgs e)
 {
     try
     {
         decimal v_dc_id_chuc_nang = Convert.ToDecimal(m_lsb_chuc_nang_chua_co.SelectedValue);
         decimal v_dc_id_nhom_nguoi_dung = Convert.ToDecimal(m_cbo_nhom_nguoi_dung.SelectedValue);
         HT_PHAN_QUYEN_NHOM v_ht_phan_quyen = new HT_PHAN_QUYEN_NHOM();
         v_ht_phan_quyen.ID_NHOM_NGUOI_DUNG = v_dc_id_nhom_nguoi_dung;
         v_ht_phan_quyen.ID_CHUC_NANG = v_dc_id_chuc_nang;
         db.HT_PHAN_QUYEN_NHOM.Add(v_ht_phan_quyen);
         db.SaveChanges();
         //reload 2 list box
         load_data_to_cbo_chuc_nang_da_co();
         load_data_to_cbo_chuc_nang_chua_co();
     }
     catch (Exception v_e)
     {
         MessageBox.Show(v_e.ToString());
     }
 }
        void m_btn_them_tat_ca_chuc_nang_Click(object sender, EventArgs e)
        {
            try
            {
                decimal v_dc_id_nhom_nguoi_dung = Convert.ToDecimal(m_cbo_nhom_nguoi_dung.SelectedValue);
                //list chuc nang chua co
                var v_lst_chuc_nang_chua_co = db.HT_CHUC_NANG
                            .Where(x => x.HT_PHAN_QUYEN_NHOM.Count(y => y.ID_NHOM_NGUOI_DUNG == v_dc_id_nhom_nguoi_dung
                                                            && y.ID_CHUC_NANG == x.ID) == 0)
                           .ToList();
                //Xoa phan quyen
                for (int i = 0; i < v_lst_chuc_nang_chua_co.Count; i++)
                {
                    HT_PHAN_QUYEN_NHOM v_ht_phan_quyen = new HT_PHAN_QUYEN_NHOM();
                    v_ht_phan_quyen.ID_NHOM_NGUOI_DUNG = v_dc_id_nhom_nguoi_dung;
                    v_ht_phan_quyen.ID_CHUC_NANG = v_lst_chuc_nang_chua_co[i].ID;
                    db.HT_PHAN_QUYEN_NHOM.Add(v_ht_phan_quyen);
                    db.SaveChanges();
                }

                //reload 2 list box
                load_data_to_cbo_chuc_nang_da_co();
                load_data_to_cbo_chuc_nang_chua_co();
            }
            catch (Exception v_e)
            {
                MessageBox.Show(v_e.ToString());
            }
        }