问如何清除购物车php

EN

/**
     * Displays the products bought from products 'added to cart'
     *
     * @Route("/bought", name="product_bought")
     * @Method("GET")
     * @Template()
     */
    public function boughtAction(Request $request) {

        $em = $this->getDoctrine()->getManager();

        $user = $this->getUser();

        $cart = $em->getRepository('ShopBundle:UserCart')->findOneBy(['user' => $this->getUser()]);

        $totalCostOfAllProducts = 0;

            $cart->getSubmitted(); //it's false
            var_dump($cart->getSubmitted());
            $cart->setSubmitted(true);
        $sub = $cart->getSubmitted(); //it's true

        if ($sub == true) {
            $cart = null;
        }
        // var_dump($cart);
        var_dump($sub);

        return array(
            'user' => $user,
            'quantity' => $cart->getQuantities(),
            'totalCostOfAllProducts' => $totalCostOfAllProducts,
        );
    }