private void ThemSach_Load(object sender, EventArgs e)
{
cbbNCC.DataSource = db.TenNCC();
cbbNCC.DisplayMember = "TenNCC";
cbbNCC.ValueMember = "MaNCC";
cbbNXB.DataSource = db.TenNXB();
cbbNXB.DisplayMember = "TenNXB";
cbbNXB.ValueMember = "MaNXB";
cbbTacGia.DataSource = db.TenTacGia();
cbbTacGia.DisplayMember = "TenTacGia";
cbbTacGia.ValueMember = "MaTacGia";
cbbChuDe.DataSource = db.Tenchude();
cbbChuDe.DisplayMember = "TenChuDe";
cbbChuDe.ValueMember = "MaChuDe";
}