在 MySQL 中模拟 DELETE CASCADE? [英] Simulate a DELETE CASCADE in MySQL?

问题描述

是否可以自动预测 DELETE CASCADE 之后的操作?在我的软件中，我想向用户发出警告，其中包含有关将被删除的数据的详细信息.

Is it possible to predict the operations that follow a DELETE CASCADE automatically? In my software I would like to give the user a warning with details about the data that would be deleted then.

推荐答案

您可以制作数据库的副本并将触发器放在删除后

You can make a copy of the database and put triggers on the after delete

DELIMITER $$

CREATE TRIGGER ad_table1_each AFTER DELETE ON table1 FOR EACH ROW
BEGIN
  INSERT INTO log VALUES (null                 /*autoinc id*/
        , 'table1'                             /*tablename*/
        , old.id                               /*tableid*/
        , concat_ws(',',old.field1,old.field2  /*CSV's of fields*/
        , NOW()                                /*timestamp*/
        , 'delete');                           /*what action*/


  REPLACE INTO restore_table1 VALUES (old.id,
        , old.field1
        , old.field2
        , ... );

END $$

DELIMITER ;

日志表只是一个包含以下字段的表:

The log table is just a table with the following fields:

id            integer autoincrement primary key
tablename     varchar(45)
table_id      integer
fields        varchar(6000)
delete_time   timestamp
action        enum('insert','update','delete')

如果在副本的删除级联之前执行 SELECT @last_id:= max(id) FROM log.
然后你可以做一个 SELECT * FROM log WHERE id >@last_id
并获取将在级联中删除的所有行.

If you do a SELECT @last_id:= max(id) FROM log before the delete cascade on the copy.
Then you can do a SELECT * FROM log WHERE id > @last_id
and get all the rows that will be deleted in the cascade.

之后，您可以使用restore_table1 在副本数据库中重新创建在级联中删除的行.

After that you can use the restore_table1 to recreate the rows that were deleted in the cascade in the copy database.

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