Method getItemsIdString

public function getItemsIdString($items)
{
    $itemsR = '';
    if (!empty($items)) {
        $itemsA = array();
        foreach ($items as $k => $v) {
            if (isset($v['product_id']) && (int) $v['product_id'] > 0) {
                $itemsA[] = $v['product_id'];
            }
        }
        $itemsR = implode(',', $itemsA);
    }
    if ($itemsR == '') {
        return false;
    }
    return $itemsR;
}