private void frmBook_Add_Load(object sender, EventArgs e)
{
lblBook_ID.Text = sach_BUS.PhatSinhMaSach();
lblBook_SeriesOfBook.Text = dauSach_BUS.PhatSinhMaDauSach();
TheLoai_BUS theLoai_BUS = new TheLoai_BUS();
comBook_Category.DataSource = theLoai_BUS.LayDSTheLoai();
comBook_Category.DisplayMember = "TenTheLoai";
comBook_Category.ValueMember = "MaTheLoai";
}