在MySQL中模擬DELETE CASCADE？

Question

是否可以自動預測DELETE CASCADE後面的操作？在我的軟件中，我想向用戶發出警告，提供有關將要刪除的數據的詳細信息。

Answer 1

可以使數據庫的副本，並把觸發器在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 ; 

日誌表僅僅是一個具有以下字段的表：

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

如果你之前做了SELECT @last_id:= max(id) FROM log副本上的刪除級聯。
然後，您可以執行SELECT * FROM log WHERE id > @last_id
並獲取將在級聯中刪除的所有行。

之後，您可以使用restore_table1重新創建複製數據庫中級聯中已刪除的行。

Answer 2

我認爲您可以將Johan的觸發解決方案與您回滾的交易結合使用。這樣可以避免需要第二個數據庫以及手動還原已刪除的條目。

• 添加觸發器和日誌表
• 每個試圖刪除啓動事務，並刪除條目
• 呈現來自日誌的信息，您的用戶批准
• 如果用戶同意提交交易，否則回滾

Answer 3

我寫了一個非常快速的黑客，完全符合你在PHP中所需要的，因爲我想做的完全一樣的事情，並沒有找到任何資源的在線。

對你來說可能已經太遲了，但它可能對別人有幫助。

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!"); 
    } 
} 

想象我有一個數據庫中的「DB」被稱爲「表」的表，我想刪除一個id爲180的話，我會打電話：

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

和它打印一個包含所有行和所有將被刪除的值的完整表。

但正如我所說，這是一個非常，非常快速和骯髒的黑客攻擊。我會很高興爲任何錯誤報告（並且肯定有很多它們！）。