how to show as row_number() in codeignitier - arrays

Question

need help what wrong with my code where this my sql command where successfull run in mysql :
SELECT func_inc_var_session() As row_number ,
vruasjalan2.*
FROM vruasjalan2 Where skid = #skid
ORDER BY kategoriruasjalanid, subkategoriruasjalanid,ruasjalanid;"
but when i want to display in my controller row_number start error say"Call to undefined method Jalan_model::num_rows()"
public function ajax_list()
{
$list = $this->Jalan->get_datatables();
$data = array();
$no = $_POST['start'];
foreach ($list as $Jalan) {
$no++;
$row = array();
$row[] = $no;
$row[] = $Jalan->row_number;
$row[] = $Jalan->ruasjalanid;
$row[] = $Jalan->skid;
$data[] = $row;
}
$output = array(
"draw" => $_POST['draw'],
"recordsTotal" => $this->Jalan->count_all(),
"recordsFiltered" => $this->Jalan->count_filtered(),
"data" => $data,
);
//output to json format
echo json_encode($output);
}
}
and this is my model
public function get_list_companys()
{
$this->db->select('vruasjalan2.*');
$this->db->from($this->table);
$this->db->order_by('kategoriruasjalanid','asc');
$query = $this->db->get();
$result = $query->result();
$companys = array();
foreach ($result as $row)
{
$companys[] = $row->kategoriruasjalanid;
}
return $companys;
}
if there any expert know this problems