防止在codeigniter中直接访问url

I have made a ecommerce website, where after placing order I redirect users to success page with order number. If order number doesn't exist,then id would be passed. But there is a problem when neither there exist order number nor order id then too success page is showing some previous orders placed if direct url is pasted. Eg : www.mywebsite.com/order/success/5000, here 5000 doesn't exist so it should redirect me to 404 error page.

MY_controller

 $order_num = $this->order_model->getOrderNum($order_id);

 if(empty($order_num)){
    $order_num = $order_id.'/id';
 }

 $redirect_url = 'order/success/'.$order_num.'/';
?>
<script>
    function redirect_success(url) {
        location.assign(url);
    }
    var success = '<?=$redirect_url?>';
    redirect_success(success);
</script>

My_Model

 public function getOrderNum($order_id = ''){
   $returnVal = false;

   $sql = "SELECT order_num FROM order_table";
   $sql .= " WHERE order_id = '{$order_id}'";    

 $query  = $this->db->query($sql);

  if($query->num_rows() > 0){
     $result    = $query->result_array();
     $row       = $result[0];
     $returnVal = $row;
   }

   return $returnVal['order_num'];
 }

One way is to check in the order/success controller whether the page referer is coming from the order/place page.

So in order/success, if http_referer header is not set or not from order/place, redirect to 404.

Add in order/success/ controller:

if( !isset($_SERVER['HTTP_REFERER']) || strpos($_SERVER['HTTP_REFERER'], "order/place") === -1 ) {
    $this->load->helper('url');
    redirect('/page404');
}