Como implemento a consulta do filtro de pesquisa usando o mongodb?

    $lang_id = 2;
    $format = ''; //user not selected
    $status = ''; //user not selected
    $filter=array();
    if(!empty($lang_id))
    {
      $filter['language']=$lang_id;
    }
    if(!empty($format))
    {
      $filter['format']=$format;
    }
    if(!empty($status))
    {
      $filter['status']=$status;
    }

    $request =  $collection->find($filter);