Recursion

[Nibinaear]

I've been trying to do a recursive function and I just can't get my head around the logic of it. I've been reading an article on PHP recursion but can't seem to make it work myself.

Basically I have a nested tree of projects with infinite levels. So 1 is the root node and then there are others beneath it. Each one has a p_id (primary key) and parent_id to show who its parent is.

P.s. This is Codeigniter 2.1.0 with MySQL.

  function recursion($p_id)  
  {
    $projects = $this->get_projects( array('parent_id'=>$p_id) );
  
    if ($projects['num_rows']>0) 
    {
        foreach ( $projects['result'] as $k =>$v ) 
        {
            $children = $this->get_projects( array('parent_id'=>$v->p_id) );
        
            if ( $children['num_rows'] > 0 )
            {
              $array[ $v->p_id ] = $this->recursion( $v->p_id );
            } 
            elseif (isset($v->p_id))
            {
              $array[] = $v;
            }
        }
    }
    return (isset($array) ? $array : false);
  } 

The get_projects function just returns a list of projects restricted by certain fields. I don't think the details matter except that it ends like this:

         $query = $this->db->get();//query
         
     if(isset($options['p_id']))
             $result['result'] = $query->row();
         else
             $result['result'] = $query->result();
                
         $result['num_rows'] = $query->num_rows();

         return $result;
    } 

So you get either a result or row plus num_rows in an array. It works throughout the site.

Error

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 18 bytes) in /home/seedetai/public_html/simple_collab/system/database/DB_active_rec.php on line 84

I don't think this should be happening I think it's a logic issue with the code. I haven't tried increasing the memory limit but I'll do that if I can get the code right.