private void Store_Load(object sender, EventArgs e)
{
dgvSanPham.DataSource = db.InfoSach();
dgvSanPham.Columns[0].Visible = false;
(clbChuDe as ListBox).DataSource = db.Tenchude();
(clbChuDe as ListBox).DisplayMember = "TenChuDe";
(clbChuDe as ListBox).ValueMember = "MaChuDe";
}