Db::startTrans();
try{
  操作；
  对象->save();
  Db::commit();
}
catch (Exception $ex) {
  Db::rollback();
  throw $ex;
}

private function createOrderByTrans($snap)
{
    Db::startTrans();
    try {
      $orderNo = $this->makeOrderNo();
      $order = new OrderModel();
      $order->user_id = $this->uid;
      $order->order_no = $orderNo;
      $order->total_price = $snap['orderPrice'];
      $order->total_count = $snap['totalCount'];
      $order->snap_img = $snap['snapImg'];
      $order->snap_name = $snap['snapName'];
      $order->snap_address = $snap['snapAddress'];
      $order->snap_items = json_encode($snap['pStatus']);
      $order->save();
      $orderID = $order->id;
      $create_time = $order->create_time;
      foreach ($this->oProducts as &$p) {
        $p['order_id'] = $orderID;
      }
      $orderProduct = new OrderProduct();
      $orderProduct->saveAll($this->oProducts);
      Db::commit();
      return [
        'order_no' => $orderNo,
        'order_id' => $orderID,
        'create_time' => $create_time
      ];
    } catch (Exception $ex) {
      Db::rollback();
      throw $ex;
    }
}