CodeIgniter: ошибка CRUD order_by ⇐ Php

[Anonymous]

У меня возникла ошибка при использовании методов CRUD. Кто-нибудь может мне помочь?

JS_Model.php

class JS_Model extends CI_Model
{

protected $_table_name = '';
protected $_primary_key = 'id';
protected $_primary_filter = 'intval';
protected $_order_by = '';
protected $_rules = array();
protected $_timestamps = FALSE;

function __construct()
{
parent::__construct();
}

public function get($id = NULL, $single = FALSE)
{
if($id != NULL) {

$filter = $this->_primary_filter;
$id = $filter($id);

$this->db->where($this->_primary_key, $id);
$method = 'row';

} elseif($single == TRUE) {

$method = 'row';

} else {

$method = 'result';

}

if(!count($this->db->ar_orderby)){
$this->db->order_by($this->order_by);
}

return $this->db->get($this->_table_name)->$method();
}

public function get_by($where, $single = FALSE)
{
$this->db->where($where);

return $this->get(NULL, $single);
}

}


page_m.php

class Page_m extends JS_Model
{

protected $_table_name = 'pages';
protected $_primary_key = 'id';
protected $_primary_filter = 'intval';
protected $_order_by = 'order';
protected $_rules = array();
protected $_timestamps = FALSE;

}


page.php

class Page extends Frontend_Controller
{

public function __construct()
{
parent::__construct();

$this->load->model('page_m');
}

public function index()
{

$pages = $this->page_m->get();

//var_dump($pages);
print_r($pages);

}
}


Сообщения об ошибках приведены ниже

A PHP Error was encountered

Severity: Notice

Message: Undefined property: Page::$order_by

Filename: core/Model.php

Line Number: 51


и

A Database Error Occurred

Error Number: 1054

Unknown column '' in 'order clause'

SELECT * FROM (`pages`) ORDER BY `

Filename: C:\xampp\htdocs\my-cms\system\database\DB_driver.php

Line Number: 330


Подробнее здесь: https://stackoverflow.com/questions/201 ... r-by-error