thinkphp3.2.2try catch和mysql事务

try{
			M()->execute('begin');
			if (M('role_user')->where(array('user_id'=>$er_info['er_user_id']))->save(array('role_id'=>2))===false) {
				throw new \Exception("激活账户失败，请稍后重试");
				
			};
			M()->execute('commit');
			var_dump('激活成功');
		}catch(\Exception $e){
			M()->execute('rollback');
			die($e->getMessage());
		}