子事务处于活动状态时无法回滚 - 错误 2D000

Question

我编写了一个存储过程，它基本上循环遍历 fields 的数组，并在每次迭代时在数据库中执行一些操作。我想要实现的是，要么循环的所有迭代都应该发生，要么它们都不应该发生。

假设字段数组中有 5 个元素，循环迭代到第 3 个元素，然后发现某些条件为真并引发错误，我想回滚前 2 个期间发生的所有更改迭代。我已经使用 ROLLBACK 语句来实现相同的目的，但是每次它到达 ROLLBACK 语句时都会抛出以下错误：

Cannot rollback while a subtransaction is active : 2D000

令人惊讶的是，如果我在 EXCEPTION WHEN OTHERS THEN 块中注释掉 outobj := json_build_object('code',0); 语句或者完全删除整个块，它会正常工作。

我检查了 PostgreSQL documentation for error codes，但它并没有真正帮助。我的存储过程如下：


CREATE OR REPLACE PROCEDURE public.usp_add_fields(
    field_data json,
    INOUT outobj json DEFAULT NULL::json)
LANGUAGE 'plpgsql'
AS $BODY$
DECLARE 
v_user_id bigint;
farm_and_bussiness json;
_field_obj json;
_are_wells_inserted boolean;
BEGIN

-- get user id
 v_user_id = ___uf_get_user_id(json_extract_path_text(field_data,'user_email'));

IF(v_user_id IS NULL) THEN
    outobj := json_build_object('code',17);
    RETURN;
END IF;

-- Loop over entities to create farms & businesses
FOR _field_obj IN SELECT * FROM json_array_elements(json_extract_path(field_data,'fields'))
LOOP
    -- check if irrigation unit id is already linked to some other field
    IF(SELECT EXISTS(
        SELECT field_id FROM user_fields WHERE irrig_unit_id LIKE json_extract_path_text(_field_obj,'irrig_unit_id') AND deleted=FALSE
    )) THEN
        outobj := json_build_object('code',26);
        -- Rollback any changes made by previous iterations of loop
        ROLLBACK;
        RETURN;
    END IF;
    
    -- check if this field name already exists
    IF( SELECT EXISTS(
            SELECT uf.field_id FROM user_fields uf
            INNER JOIN user_farms ufa ON (ufa.farm_id=uf.user_farm_id AND ufa.deleted=FALSE)
            INNER JOIN user_businesses ub ON (ub.business_id=ufa.user_business_id AND ub.deleted=FALSE)
            INNER JOIN users u ON (ub.user_id = u.user_id AND u.deleted=FALSE)
            WHERE u.user_id = v_user_id
            AND uf.field_name LIKE json_extract_path_text(_field_obj,'field_name')
            AND uf.deleted=FALSE
        )) THEN 
        outobj := json_build_object('code', 22);
        -- Rollback any changes made by previous iterations of loop
        ROLLBACK;
        RETURN;
    END IF;

    --create/update user business and farm and return farm_id 
    CALL usp_add_user_bussiness_and_farm(
        json_build_object('user_email', json_extract_path_text(field_data,'user_email'),
                          'business_name', json_extract_path_text(_field_obj,'business_name'),
                          'farm_name', json_extract_path_text(_field_obj,'farm_name')
        ), farm_and_bussiness);

    IF(json_extract_path_text(farm_and_bussiness, 'code')::int != 1) THEN
        outobj := farm_and_bussiness;
        -- Rollback any changes made by previous iterations of loop
        ROLLBACK;
        RETURN;
    END IF;

    -- insert into users fields
    INSERT INTO user_fields (user_farm_id, irrig_unit_id, field_name, ground_water_percent, surface_water_percent)
    SELECT json_extract_path_text(farm_and_bussiness,'farm_id')::bigint,
    json_extract_path_text(_field_obj,'irrig_unit_id'),
    json_extract_path_text(_field_obj,'field_name'),
    json_extract_path_text(_field_obj,'groundWaterPercentage'):: int,
    json_extract_path_text(_field_obj,'surfaceWaterPercentage'):: int;

    -- add to user wells
    CALL usp_insert_user_wells(json_extract_path(_field_obj,'well_data'), v_user_id, _are_wells_inserted);
END LOOP;

outobj := json_build_object('code',1);
RETURN;

EXCEPTION WHEN OTHERS THEN 
    raise notice '% : %', SQLERRM, SQLSTATE;
    outobj := json_build_object('code',0);
RETURN;

END;
$BODY$;

Answer 1

如果您在 PL/pgSQL 块中有一个 EXCEPTION 子句，则整个块将在一个子事务中执行，该子事务在发生异常时回滚。所以你不能在这样的块中使用 COMMIT 或 ROLLBACK。

如果您确实需要 ROLLBACK，请像这样重写您的代码：

DECLARE
   should_rollback boolean := FALSE;
BEGIN
   FOR ... LOOP
      BEGIN  -- inner block for exception handling
         /* do stuff */
         IF (/* condition that should cause a rollback */) THEN
            should_rollback := TRUE;
            EXIT;  -- from LOOP
         END IF;
      EXCEPTION
         WHEN OTHERS THEN
            /* handle the error */
      END;
   END LOOP;

   IF should_rollback THEN
      ROLLBACK;
      /* do whatever else is needed */
   END IF;
END;

现在回滚不会发生在带有异常处理程序的块中，它应该按照您想要的方式工作。

Answer 2

解释：

根据@Laurez Albe提供的线索，我想出了一个更简洁的方法来解决上述问题。

基本上，我所做的是，只要条件为 true，我就会提出 custom exception。所以当抛出异常时，block X所做的所有更改都会优雅地回滚。我什至可以在异常条件块中执行最后一分钟的清理。

实施：

CREATE OR REPLACE procedure mProcedure(INOUT resp json DEFAULT NULL::JSON)
LANGUAGE 'plpgsql'
AS $BODY$
DECLARE
field_data json := '{ "fields": [1,2,3,4,5] }';
_field_id int;
BEGIN

-- Start of block X
FOR _field_id IN SELECT * FROM json_array_elements(json_extract_path(field_data,'fields'))
LOOP
    INSERT INTO demo VALUES(_field_id);
    
    IF(_field_id = 3) THEN
      RAISE EXCEPTION USING ERRCODE='22013';
    END IF;
   
    IF(_field_id = 5) THEN
      RAISE EXCEPTION USING ERRCODE='22014';
    END IF;
END LOOP;

SELECT json_agg(row_to_json(d)) INTO resp FROM demo d;
RETURN;
-- end of block X


-- if an exception occurs in block X, then all the changes made within the block are rollback
-- and the control is passed on to the EXCEPTION WHEN OTHERS block.  
EXCEPTION 
WHEN sqlstate '22013' THEN
resp := json_build_object('code',26);

WHEN sqlstate '22014' THEN
resp := json_build_object('code',22);

END;
$BODY$;

演示：

Dbfiddle

子事务处于活动状态时无法回滚 - 错误 2D000

Cannot rollback while a subtransaction is active - Error 2D000

sql

postgresql

plpgsql

解释：

实施：

演示：