PostgreSQL无法在PL / pgSQL中开始/结束事务

发布时间：2020-12-13 16:29:38 所属栏目：百科来源：网络整理

导读：我正在寻求澄清如何确保plpgsql函数中的原子事务,以及为数据库进行此特定更改设置了隔离级别. 在下面显示的plpgsql函数中,我想确保BOTH的删除和插入成功.当我尝试将它们包装在一个事务中时,我收到一个错误：错误：无法在PL / pgSQL中开始/结束事务. 如果另

我正在寻求澄清如何确保plpgsql函数中的原子事务,以及为数据库进行此特定更改设置了隔离级别.

在下面显示的plpgsql函数中,我想确保BOTH的删除和插入成功.当我尝试将它们包装在一个事务中时,我收到一个错误：
错误：无法在PL / pgSQL中开始/结束事务.

如果另一个用户在此功能已删除自定义记录之后,但在此函数有机会插入自定义记录之前,为情况(RAIN,NIGHT,45MPH)添加了默认行为,下面的函数执行过程中会发生什么？是否有一个隐式事务包装插入和删除,以便如果另一个用户已经更改了此函数引用的任何一个行,两者都将回滚？我可以设置此功能的隔离级别吗？

create function foo(v_weather varchar(10),v_timeofday varchar(10),v_speed varchar(10),v_behavior varchar(10))
     returns setof CUSTOMBEHAVIOR
     as $body$
     begin

        -- run-time error if either of these lines is un-commented

        -- start transaction ISOLATION LEVEL READ COMMITTED;
        -- or,alternatively,set transaction ISOLATION LEVEL READ COMMITTED;


         delete from CUSTOMBEHAVIOR 
         where weather = 'RAIN' and timeofday = 'NIGHT' and speed= '45MPH' ;

        -- if there is no default behavior insert a custom behavior

        if not exists
          (select id from DEFAULTBEHAVIOR where a = 'RAIN' and b = 'NIGHT' and c= '45MPH') then   
           insert into CUSTOMBEHAVIOR
             (weather,timeofday,speed,behavior)
           values
             (v_weather,v_timeofday,v_speed,v_behavior);
       end if;

       return QUERY
       select * from CUSTOMBEHAVIOR where ...   ;


      -- commit;


     end
     $body$
     LANGUAGE plpgsql

一个plpgsql函数在事务中自动运行.这一切都成功了,一切都失败了.

我引用the manual on plpgsql functions：

Functions and trigger procedures are always executed within a
transaction established by an outer query — they cannot start or
commit that transaction,since there would be no context for them to
execute in. However,a block containing an EXCEPTION clause
effectively forms a subtransaction that can be rolled back without
affecting the outer transaction.

所以,如果你需要,你可以捕获理论上可能发生的异常(但是不大可能).
Details on trapping errors in the manual.

您的功能审查和简化：

CREATE FUNCTION foo(v_weather text,v_timeofday text,v_speed text,v_behavior text)
  RETURNS SETOF custombehavior AS
$body$
BEGIN

DELETE FROM custombehavior
WHERE  weather = 'RAIN'
AND    timeofday = 'NIGHT'
AND    speed = '45MPH';

INSERT INTO custombehavior (weather,behavior)
SELECT v_weather,v_behavior
WHERE NOT EXISTS (
   SELECT 1 FROM defaultbehavior
   WHERE  a = 'RAIN'
   AND    b = 'NIGHT'
   AND    c = '45MPH'
   );

RETURN QUERY
SELECT * FROM custombehavior WHERE ... ;

END
$body$LANGUAGE plpgsql

（编辑：李大同）

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