问题描述

假设我们有以下表结构:

Let's say we have the following table structures:

documents      docmentStatusHistory      status
+---------+   +--------------------+    +----------+
| docId   |   | docStatusHistoryId |    | statusId |
+---------+   +--------------------+    +----------+
| ...     |   | docId              |    | ...      |
+---------+   | statusId           |    +----------+
              | ...                |
              +--------------------+

可能很明显，但值得一提的是，文档的当前状态是最后输入的状态历史记录.

It may be obvious, but it's worth mentioning, that the current status of a document is the last Status History entered.

系统的性能缓慢但肯定会下降，我建议将上述结构更改为:

The system was slowly but surely degrading in performance and I suggested changing the above structure to:

documents           docmentStatusHistory      status
+--------------+   +--------------------+    +----------+
| docId        |   | docStatusHistoryId |    | statusId |
+--------------+   +--------------------+    +----------+
| currStatusId |   | docId              |    | ...      |
| ...          |   | statusId           |    +----------+
+--------------+   | ...                |
                   +--------------------+

这样我们就可以在应有的位置获得文档的当前状态.

This way we'd have the current status of a document right where it should be.

由于遗留应用程序的构建方式，我无法更改遗留应用程序的代码以更新文档表上的当前状态.

Because the way the legacy applications were built I could not change the code on legacy applications to update the current status on the document table.

在这种情况下，我不得不为我的规则打开一个例外，以不惜一切代价避免触发器，仅仅是因为我无法访问遗留应用程序代码.

In this case I had to open an exception to my rule to avoid triggers at all costs, simply because I don't have access to the legacy applications code.

我创建了一个触发器，每次将新状态添加到状态历史记录时，它都会更新文档的当前状态，它的作用就像一个魅力.

I created a trigger that updates the current status of a document every time a new status is added to the status history, and it works like a charm.

然而，在一个晦涩且很少使用的情况下，需要删除最后一个状态历史记录，而不是简单地添加一个新的.所以，我创建了以下触发器:

However, in an obscure and rarely used situation there is a need to DELETE the last status history, instead of simply adding a new one. So, I created the following trigger:

create or replace trigger trgD_History
 after delete on documentStatusHistory
 for each row
 currentStatusId number;
begin

  select statusId
    into currentStatusId
    from documentStatusHistory
   where docStatusHistoryId = (select max(docStatusHistoryId)
                                 from documentStatusHistory
                                where docId = :old.docId);

  update documentos
     set currStatusId = currentStatusId
   where docId = :old.docId;
end;

这就是我遇到臭名昭著的错误 ORA-04091 的地方.

And thats where I got the infamous error ORA-04091.

我明白为什么我收到此错误，即使我将触发器配置为 AFTER 触发器.

I understand WHY I'm getting this error, even though I configured the trigger as an AFTER trigger.

问题是我看不到解决此错误的方法.我在网上搜索了一段时间，目前没有找到任何有用的东西.

The thing is that I can't see a way around this error. I have searched the net for a while and couldn't find anything helpful so far.

及时，我们将使用 Oracle 9i.

In time, we're using Oracle 9i.

推荐答案

变异表错误的标准解决方法是创建

The standard workaround to a mutating table error is to create

• 一个包含一组密钥的包(即本例中的 docId).临时表也可以使用
• 初始化集合的 before 语句触发器
• 一个行级触发器，使用每个已更改的 docId 填充集合
• 一个 after 语句触发器，它遍历集合并执行实际的 UPDATE

有点像

CREATE OR REPLACE PACKAGE pkg_document_status
AS
  TYPE typ_changed_docids IS TABLE OF documentos.docId%type;
  changed_docids typ_changed_docids := new typ_changed_docids ();

  <<other methods>>
END;

CREATE OR REPLACE TRIGGER trg_init_collection
  BEFORE DELETE ON documentStatusHistory
BEGIN
  pkg_document_status.changed_docids.delete();
END;

CREATE OR REPLACE TRIGGER trg_populate_collection
  BEFORE DELETE ON documentStatusHistory
  FOR EACH ROW
BEGIN
  pkg_document_status.changed_docids.extend();
  pkg_document_status.changed_docids( pkg_document_status.changed_docids.count() ) := :old.docId;
END;

CREATE OR REPLACE TRIGGER trg_use_collection
  AFTER DELETE ON documentStatusHistory
BEGIN
  FOR i IN 1 .. pkg_document_status.changed_docids.count()
  LOOP
    <<fix the current status for pkg_document_status.changed_docids(i) >>
  END LOOP;
  pkg_document_status.changed_docids.delete();
END;

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