recursive function in codeigniter returns 500 error

Question

i have this next recursive function that keep return 500 error

public function get_parent($cat=0){
        $ci = &get_instance();
        $q= $ci->db->query("SELECT category_id,parent_id FROM tbl_products_categories WHERE  category_id = {$cat}");
        if($q->num_rows()>0){
            $row = $q->row();
            if($row->parent_id == 0){
                return $row->category_id;
                break;
            }else if($row->parent_id != 0){
                 $this->get_parent($row->category_id) ;
            }
        }
        else{
            return 0;
        }

    }

i am calling the function like this:

$cat = 9;
$main_cat =$this->get_parent($cat);

Answer 1

$this->get_parent($row->category_id);

is calling get_parent with the same ID you originally called it with so it keep recursing until you get a stack overflow.

FYI Depending on your database, it should be possible to do what you want in pure SQL without multiple queries.

Edit: Also, you probably want to do

$ci->db->query("SELECT category ... WHERE category_id=?", array($cat));

instead of what you have now because your current query is susceptable to SQL injection if your function is called with anything other than a number.