public function checkout()
    {
        if (!class_exists($this->config()->checkout_class)) {
            return $this->httpError(404);
        }

        $checkout = Injector::inst()
            ->get($this->config()->checkout_class);
        $checkout->setEstimate($this->dataRecord);

        $this->extend("onBeforeCheckout");

        $this->redirect($checkout->Link());
    }