$em = $this->getDoctrine()->getEntITyManager();
$city = 'new york';
$minPRice = 500;
$maxprice = 1000;

$testquery = "SELECT p From AcmeTestBundle:Car p WHERE p.city = :city";
$testparam = array('city' => $city,);

if ($minprice != '') {
    if ($maxprice != '') {
        $testquery .= " and p.price BETWEEN :minprice AND :maxprice";
        $testparam .= array(
            'minprice' => $minprice,'maxprice' => $maxprice,);
    }
}

$testquery .= " ORDER BY p.price ASC";

$query = $em->createQuery($testquery)->setParameters($testparam);

$result = $query->getResult();

有一个更好的方法吗？