Oracle 删除触发器后...如何避免变异表 (ORA-04091)？

Oracle After Delete Trigger... How to avoid Mutating Table (ORA-04091)?

提问by Paulo Santos

Let's say we have the following table structures:

假设我们有以下表结构：

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

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

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。

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

该系统的性能缓慢但肯定会下降，我建议将上述结构更改为：

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

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

通过这种方式，我们可以将文档的当前状态放在应有的位置。

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.

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来更新文档表上的当前状态。

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.

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。

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.

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都会更新文档的当前状态，它的作用就像一个魅力。

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

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，而不是简单地添加一个新的。所以，我创建了以下触发器：

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;

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

这就是我得到臭名昭著的错误的地方ORA-04091。

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

我明白为什么我会收到这个错误，即使我将触发器配置为AFTER触发器。

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.

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，到目前为止找不到任何有用的东西。

In time, we're using Oracle 9i.

随着时间的推移，我们正在使用 Oracle 9i。

回答by Justin Cave

The standard workaround to a mutating table error is to create

变异表错误的标准解决方法是创建

• A package with a collection of keys (i.e. docId's in this case). A temporary table would also work
• A before statement trigger that initializes the collection
• A row-level trigger that populates the collection with each docId that has changed
• An after statement trigger that iterates over the collection and does the actual UPDATE

• 带有一组键的包（即本例中的 docId）。临时表也可以
• 初始化集合的 before 语句触发器
• 使用已更改的每个 docId 填充集合的行级触发器
• 迭代集合并执行实际 UPDATE 的 after 语句触发器

So something like

所以像

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;

回答by HAL 9000

seems to be a duplicate of this question

似乎是这个问题的重复

check out Tom Kyte's take on that

看看Tom Kyte 对此的看法