ORA-04091: 表名发生变化 - 当来自子表的触发器想要更新父表时

Question

我有 2 个简单的表格：

CREATE TABLE ORDERS
( ORDER_KEY number(10) NOT NULL,
  ORDER_NR varchar2(50) NOT NULL,
  LAST_UPDATE DATE,
  CONSTRAINT ORDERS_PK PRIMARY KEY (ORDER_KEY)
);

CREATE TABLE ORDER_POSITIONS
( ORDER_POS_KEY number(10) NOT NULL,
  ORDER_POS_NR number(10),
  ORDER_POS_DESCRIPTION varchar2(50),
  ORDER_KEY NUMBER(10) NOT NULL,
  CONSTRAINT ORDER_POSITIONS_PK PRIMARY KEY (ORDER_POS_KEY),
  CONSTRAINT ORDERS_FK
    FOREIGN KEY (ORDER_KEY)
    REFERENCES ORDERS(ORDER_KEY)
    ON DELETE CASCADE
);

在 ORDER_POSITIONS 表上，我创建了一个触发器，该触发器应在删除位置时更新 LAST_UPDATE 列。

CREATE OR REPLACE TRIGGER TGAUDIT_ORDER_POS
AFTER DELETE
    ON ORDER_POSITIONS 
FOR EACH ROW

DECLARE

BEGIN
    UPDATE ORDERS O SET O.LAST_UPDATE = SYSDATE WHERE O.ORDER_KEY = :OLD.ORDER_KEY;   
END;

如果我从表 ORDER_POSITION 中删除一个位置，一切正常（LAST_UPDATE 列已更新）。

但是，如果我想删除一个订单，它的所有仓位也会被删除（通过 CASCADE DELETE）。此时，表 ORDER_POSITIONS 上的触发器也被引发，它想要更新当前正在删除的表的列 - ORDERS。显然我得到了错误：ORA-04091 Table ORDERS is mutating.

有办法解决吗？

Answer 1

我终于用复合触发器解决了：

CREATE OR REPLACE TRIGGER TGAUDIT_ORDER_POS
  FOR DELETE ON ORDER_POSITIONS
    COMPOUND TRIGGER
     
    TYPE parent_key_type IS TABLE OF ORDERS.ORDER_KEY%TYPE;
    parent_keys parent_key_type := parent_key_type();
    
    AFTER EACH ROW IS BEGIN
      IF DELETING THEN 
        BEGIN 
          parent_keys.extend;
          parent_keys(parent_keys.last) := :old.ORDER_KEY;
        END;
      END IF;
    END AFTER EACH ROW;
    
    AFTER STATEMENT IS BEGIN
      FOR i IN 1..parent_keys.count LOOP
        UPDATE DEVART_TEST.ORDERS O SET O.LAST_UPDATE = SYSDATE WHERE O.ORDER_KEY = parent_keys(i);   
      END LOOP;
    END AFTER STATEMENT;
    
END;

更新：另一种选择是在常规触发器中捕获此特定异常。

CREATE OR REPLACE TRIGGER TGAUDIT_ORDER_POS
AFTER DELETE
  ON ORDER_POSITIONS 
  FOR EACH ROW

  DECLARE
    TABLE_MUTATING EXCEPTION;
    PRAGMA EXCEPTION_INIT(TABLE_MUTATING, -4091 );

BEGIN
    UPDATE ORDERS O SET O.LAST_UPDATE = SYSDATE WHERE O.ORDER_KEY = :OLD.ORDER_KEY;   
    EXCEPTION 
      WHEN TABLE_MUTATING THEN 
        NULL; -- suppress 
END;

Answer 2

我将重新创建没有ON DELETE CASCADE 子句的外键约束，并在删除订单之前删除所有订单位置。这样，您就可以避免两个表同时发生变异，从而避免变异表错误。