$m = new MongoClient();
$db = $m->selectDB('testDB');
$collection = new MongoCollection($db, 'test_insert');
$filter= array('response' => array('$elemMatch' => array('categoryId' => 'road')));
$z=$collection->find($filter);
var_dump($z)
db.test_insert.find({response:{$elemMatch:{categoryId:'road'}}})