function addToCart($product_id, $session_id, $user_id = null)
{
$time = new TimeHelper();
$this->data['Cart']['product_id'] = $product_id;
$this->data['Cart']['ct_date'] = $time->format("Y-m-d H:i:s", $time->gmt());
$this->data['Cart']['ct_qty'] = 1;
$this->data['Cart']['ct_session_id'] = $session_id;
$this->data['Cart']['user_id'] = $user_id;
$this->save();
}
