Menus_model::updateStock PHP Method

    public function updateStock($menu_id, $quantity = 0, $action = 'subtract')
    {
        $update = FALSE;
        if (is_numeric($menu_id)) {
            $this->db->select('menus.menu_id, menu_name, stock_qty, minimum_qty, subtract_stock, menu_status');
            $this->db->from('menus');
            $this->db->where('menus.menu_id', $menu_id);
            $query = $this->db->get();
            if ($query->num_rows() > 0) {
                $row = $query->row_array();
                if ($row['subtract_stock'] === '1' and !empty($quantity)) {
                    $stock_qty = 'stock_qty + ' . $quantity;
                    if ($action === 'subtract') {
                        $stock_qty = 'stock_qty - ' . $quantity;
                    }
                    $this->db->set('stock_qty', $stock_qty, FALSE);
                    $this->db->where('menu_id', $menu_id);
                    $update = $this->db->update('menus');
                }
            }
        }
        return $update;
    }