代码示例如下：
// 事务处理 派单表(主表)
$model = M('sendorders');
$model->startTrans(); // 开启事务
$user = $model->lock(true)->where(array('id'=>$sendid))->getField('orderstate');
if( $user === '1' || $user === '5' ){
// 修改 派单表(主表) 抢单状态、司机id
$model->where(array('id'=>$sendid))->save(array('orderstate'=>'2','driveid'=>$userid));
// 修改 派单表(副本)抢单成功，司机的接单状态
$Model_up = new \Think\Model(); // 实例化一个model对象 没有对应任何数据表
$Model_up->execute("UPDATE db_orders,db_driver SET db_orders.state = '2',db_driver.condition = '2' WHERE db_orders.sendid = '$sendid' AND db_orders.userid = '$userid' AND db_driver.id = '$userid' ");
$model->commit(); // 开启事务
echo json_encode(['code'=>200,'message'=>'成功']);
}else{
$model->rollback(); // 回滚
echo json_encode(['code' => 311, 'message' => '已被接单了！！']);die;
} 