private void btnThemDT_Click(object sender, EventArgs e)
        {
            string maDT = maDeThiTextBox.Text;

            maDeThiTextBox.Undo();
            if (_deThiRepository.FindByCondition(p => p.MaDeThi.Equals(maDT)).Count() > 0)
            {
                MessageBox.Show("Mã đề thi đã tồn tại", "Lỗi", MessageBoxButtons.OK, MessageBoxIcon.Error);;
                return;
            }
            _deThiRepository = new DeThiRepository();
            DeThi deThi = new DeThi();

            deThi.MaDeThi  = maDT;
            deThi.TenDeThi = tenDeThiTextBox.Text;
            deThi.MaMH     = maMHComboBox.SelectedValue.ToString();
            deThi.ThoiGian = int.Parse(thoiGianTextBox.Text);
            deThi.MaCapHoc = int.Parse(maCapHocComboBox.SelectedValue.ToString());
            deThi.MaGV     = lblMaGV.Text;
            deThi.NgayTao  = DateTime.Now;

            _deThiRepository.Create(deThi);
            _deThiRepository.Update();


            foreach (DataGridViewRow item in dgvDSCauHoi.Rows)
            {
                var cell = item.Cells["Chon"] as DataGridViewCheckBoxCell;
                if (cell.Value == cell.TrueValue)
                {
                    string cauhoi   = item.Cells["DeThiCauHoi"].Value.ToString();
                    CauHoi idCauHoi = _cauHoiRepository.FindByCondition(p => p.CauHoiDeBai.Equals(cauhoi)).Single();
                    _dt_chRepository.Create(new DeThi_CauHoi
                    {
                        MaDT     = maDT,
                        IDCauHoi = idCauHoi.IDCauHoi
                    });
                }
            }
            _dt_chRepository.Update();
            ReLoad();
        }