public ThueSach TraSach(int makhachhang, int masach)
 {
     if (GetSachById(masach) != null)
     {
         KhachHangService khachHangService = new KhachHangService();
         if (khachHangService.GetKhachHangById(makhachhang) != null)
         {
             ThueSach thueSach = GetThueSachKhach(makhachhang, masach);
             if (thueSach != null)
             {
                 thueSach.TinhTrang = "0";
                 Sach sach = GetSachById(masach);
                 sach.SoLuong = (Convert.ToInt32(sach.SoLuong) + 1).ToString();
                 qLTV.SaveChanges();
                 return(thueSach);
             }
             ;
             return(null);
         }
         return(null);
     }
     return(null);
 }