private void btnDone_Click(object sender, EventArgs e)
        {
            if (!IsValidTextBox())
            {
                return;
            }

            DTO.SachDTO book = new DTO.SachDTO
            {
                Ma           = GenerateBookId(),
                Ten          = txtTitle.Text,
                MaTheLoai    = cbCategory.SelectedValue.ToString(),
                MaTacGia     = cbAuthor.SelectedValue.ToString(),
                MaMXB        = cbPublisher.SelectedValue.ToString(),
                NgayXuatBan  = dtpPublicationDate.Value,
                GiaTien      = double.Parse(txtPrice.Text),
                ViTri        = txtPosition.Text,
                NgayTiepNhan = dtpReceivedDate.Value,
                MaNVTiepNhan = cbbTaker.SelectedValue.ToString()
            };

            int result = bUS.AddANewBook(book);

            if (1 == result)
            {
                MessageBox.Show("Thành công!");
            }
            else
            {
                MessageBox.Show("Thất bại!");
            }

            txtTitle.Text    = "";
            txtPosition.Text = "";
            txtPrice.Text    = "";
        }