在MySQL中模拟删除级联?

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.

是否有可能自动预测删除级联之后的操作?在我的软件中，我想给用户一个警告，详细说明将要删除的数据。

3 个解决方案

#1

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

您可以复制数据库并将触发器放在after delete上

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 ;

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

日志表只是一个包含以下字段的表:

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

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.

如果在拷贝上的删除级联之前从日志中选择@last_id:= max(id)。然后，您可以从日志中选择id > @last_id并获取在级联中删除的所有行。

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

之后，可以使用restore_table1重新创建复制数据库中级联中删除的行。

#2

I think you could use Johan's trigger solution in combination with a transaction that you roll back. This avoids both the need for a second database and for the manual restore of the deleted entries.

我认为您可以结合使用Johan的触发器解决方案和回滚的事务。这既避免了需要第二个数据库，也避免了手动恢复已删除条目。

• add the trigger and the log table
• 添加触发器和日志表
• for each attempted deletion start a transaction and delete the entries
• 对于每一个尝试的删除，启动一个事务并删除条目。
• present the information from the log to your user for approval
• 将日志中的信息显示给用户以供批准
• if the user agrees commit the transaction, otherwise rollback
• 如果用户同意提交事务，则回滚

#3

I wrote a very quick hack that does exactly what you need in PHP, since I wanted to do the exact same thing and haven't found any resources for that online.

我写了一个非常快速的技巧，它完全满足PHP的需要，因为我想做同样的事情，而且还没有找到任何在线的资源。

It might be too late for you, but it may help others.

对你来说可能太晚了，但它可能会帮助别人。

function get_referencing_foreign_keys ($database, $table) {
    $query = 'SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE REFERENCED_TABLE_SCHEMA = "'.$database.'" AND REFERENCED_TABLE_NAME = '.esc($table);
    $result = rquery($query);
    $foreign_keys = array();
    while ($row = mysql_fetch_row($result)) {
        $foreign_keys[] = array('database' => $row[0], 'table' => $row[1], 'column' => $row[2], 'reference_column' => $row[3]);
    }

    return $foreign_keys;
}

function get_foreign_key_deleted_data_html ($database, $table, $where) {
    $data = get_foreign_key_deleted_data ($database, $table, $where);

    $html = '';
    foreach ($data as $key => $this_data) {
        $html .= "<h2>$key</h2>\n";

        $html .= "<table>\n";
        $i = 0;
        foreach ($this_data as $value) {
            if($i == 0) {
                $html .= "\t<tr>\n";
                foreach ($value as $column => $column_value) {
                    $html .= "\t\t<th>".htmlentities($column)."</th>\n";
                }
                $html .= "\t</tr>\n";
            }
            $html .= "\t<tr>\n";
            foreach ($value as $column => $column_value) {
                $html .= "\t\t<td>".htmlentities($column_value)."</td>\n";
            }
            $html .= "\t</tr>\n";
            $i++;
        }
        $html .= "</table>\n";
    }

    return $html;
}

function get_foreign_key_deleted_data ($database, $table, $where) {
    $GLOBALS['get_data_that_would_be_deleted'] = array();
    $data = get_data_that_would_be_deleted($database, $table, $where);
    $GLOBALS['get_data_that_would_be_deleted'] = array();
    return $data;
}

function get_data_that_would_be_deleted ($database, $table, $where, $recursion = 100) {
    if($recursion <= 0) {
        die("Deep recursion!");
    }

    if($recursion == 100) {
        $GLOBALS['get_data_that_would_be_deleted'] = array();
    }

    if($table) {
        if(is_array($where)) {
            $foreign_keys = get_referencing_foreign_keys($database, $table);
            $data = array();

            $query = 'SELECT * FROM `'.$table.'`';
            if(count($where)) {
                $query .= ' WHERE 1';
                foreach ($where as $name => $value) {
                    $query .= " AND `$name` = ".esc($value);
                }
            }
            $result = rquery($query);

            $to_check = array();

            while ($row = mysql_fetch_row($result)) {
                $new_row = array();
                $i = 0;
                foreach ($row as $this_row) {
                    $field_info = mysql_fetch_field($result, $i);
                    $new_row[$field_info->name] = $this_row;
                    foreach ($foreign_keys as $this_foreign_key) {
                        if($this_foreign_key['reference_column'] == $field_info->name) {
                            $to_check[] = array('value' => $this_row, 'foreign_key' => array('table' => $this_foreign_key['table'], 'column' => $this_foreign_key['column'], 'database' => $this_foreign_key['database']));
                        }
                    }
                    $i++;
                }
                $GLOBALS['get_data_that_would_be_deleted'][$table][] = $new_row;
            }
            foreach ($to_check as $this_to_check) {
                if(isset($this_to_check['value']) && !is_null($this_to_check['value'])) {
                    get_data_that_would_be_deleted($database, $this_to_check['foreign_key']['table'], array($this_to_check['foreign_key']['column'] => $this_to_check['value']), $recursion - 1);;
                }
            }

            $data = $GLOBALS['get_data_that_would_be_deleted'];

            return $data;
        } else {
            die("\$where needs to be an array with column_name => value pairs");
        }
    } else {
        die("\$table was not defined!");
    }
}

Imagine I have a table called "table" in the database "db" and I want to delete the one with the id 180, then I'd call:

假设我在数据库中有一个名为“table”的表，我想要删除id为180的表，然后调用:

print(get_foreign_key_deleted_data_html('db', 'table', array('id' => 180)));

and it prints a full table with all the rows and all the values that would be deleted.

它打印出一个包含所有行和所有将要删除的值的完整的表。

But as I've said, this is a very, very quick and dirty hack. I'd be glad for any bug-report (and there surely are a lot of them!).

但是就像我说的，这是一个非常，非常快而且肮脏的方法。我很高兴有任何错误报告(肯定有很多!)