在 MySQL 中模擬 DELETE CASCADE？

Question

是否可以自動預測 DELETE CASCADE 之后的操作？ 在我的軟件中，我想向用戶發出警告，其中包含有關將被刪除的數據的詳細信息。

Answer 1

您可以復制數據庫並after delete放置觸發器

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 ;

日志表只是一個包含以下字段的表：

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

如果在副本上的刪除級聯之前執行SELECT @last_id:= max(id) FROM log 。
然后你可以做一個SELECT * FROM log WHERE id > @last_id
並獲取將在級聯中刪除的所有行。

之后，您可以使用 restore_table1 在副本數據庫中重新創建在級聯中刪除的行。

Answer 2

我認為您可以將 Johan 的觸發器解決方案與您回滾的事務結合使用。 這既避免了對第二個數據庫的需要，也避免了手動恢復已刪除條目的需要。

• 添加觸發器和日志表
• 為每次嘗試刪除啟動一個事務並刪除條目
• 將日志中的信息呈現給您的用戶以供批准
• 如果用戶同意提交事務，否則回滾

Answer 3

我寫了一個非常快速的 hack，它完全可以滿足您在 PHP 中的需求，因為我想做完全相同的事情並且還沒有在網上找到任何相關資源。

對你來說可能為時已晚，但它可能會幫助其他人。

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!");
    }
}

想象一下，我在數據庫“db”中有一個名為“table”的表，我想刪除 ID 為 180 的表，然后我會調用：

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

它會打印一個包含所有行和所有將被刪除的值的完整表格。

但正如我所說，這是一個非常非常快速和骯臟的黑客。 我很高興收到任何錯誤報告（而且肯定有很多！）。