外键配置双CASCADE可删父行但更新主键报1451错误求助

已尝试所有可检索到的相关解决方案，均未解决问题。
核心操作需求：更新classroom表的主键code_class，该字段同时是reservation表的外键关联字段。执行更新操作时持续返回如下报错：

Warning: PDOStatement::execute(): SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails (ebooking.reservation, CONSTRAINT reservation_ibfk_3 FOREIGN KEY (code_class) REFERENCES classroom (code_class) ON DELETE CASCADE ON UPDATE CASCADE) in C:\wamp64\www\last\ebooking2\profile\admin\updateClass.php on line 38

异常矛盾点：对同一条code_class记录执行删除操作可正常生效，按照报错信息标注，该外键确实同时配置了ON DELETE CASCADE与ON UPDATE CASCADE规则。

班级更新逻辑PHP代码 #

$requete = $bdd->prepare('SELECT * FROM classroom Where code_class = :C ');
$requete->execute(array('C'=> $CR));
          while ($donnees = $requete->fetch()){
            if (isset($_POST) & !empty($_POST)) {
                $data = [
                    'name' => $_POST['Code'],
                    'surname' => $_POST['STIME'],
                    'floor' => $_POST['fTIME'],
                    'roomtp' => $_POST['ETIME'],
                    'hard'=> $_POST['HARD'],
                    'id' => $CR,
                ];
                $sql = "UPDATE classroom SET code_class=:name,capacity=:surname,floor=:floor,room_type=:roomtp,
                hardware_type=:hard WHERE code_class=:id ";
                $stmt= $bdd->prepare($sql);
                $stmt->execute($data);
                // echo "<script>window.location.assign('hardware.php')</script>";
            }

班级删除逻辑PHP代码 #

<?php
// error_reporting(0);
session_start();
include('../../connexionDB.php');
if(!isset($_SESSION['CR']) ||$_SESSION['CR'] == ""){
   echo 'no id found';
}else {
    $AS = $_SESSION['CR'];
  
}
echo $AS;
$sql = "DELETE FROM `classroom` WHERE code_class =:c ";
    $statement = $bdd->prepare($sql);
$statement->bindParam('c', $AS);

// execute the statement
if ($statement->execute()) {
    echo 'publisher id  was deleted successfully.';
 
      }
?>

外键创建SQL语句 #

ALTER TABLE `reservation` ADD FOREIGN KEY (`code_class`) REFERENCES `classroom`(`code_class`) ON DELETE CASCADE ON UPDATE CASCADE;

核心故障原因 #

删除操作可正常触发级联规则，说明你当前看到的reservation_ibfk_3外键的DELETE CASCADE逻辑正常，但UPDATE CASCADE未生效，根因是reservation表上存在冗余外键约束：
之前创建过同字段关联、未配置ON UPDATE CASCADE规则的外键，后续执行ADD FOREIGN KEY语句时MySQL不会覆盖旧约束，而是新增约束。更新主键时，未配置级联更新的旧约束先触发校验，直接抛出1451错误。

验证方法 #

执行SQL语句SHOW CREATE TABLE reservation;，查看返回的表结构定义，你会发现reservation表上不止一个关联code_class指向classroom表的外键，其中至少有一个外键未配置ON UPDATE CASCADE规则。

修复步骤 #

• 清理冗余外键：把reservation表上所有关联code_class指向classroom表的外键全部删除，参考语句：ALTER TABLE reservation DROP FOREIGN KEY reservation_ibfk_3;，如果查到其他同关联的外键，按相同语法一并删除。
• 重建外键：重新执行你之前写的外键创建语句，确保表上只有一个配置了ON DELETE CASCADE ON UPDATE CASCADE规则的关联外键。
• 修复代码逻辑bug：更新逻辑中判断表单提交的代码用了位运算符&，需要替换为逻辑运算符&&，位运算在POST参数为空时会出现判断逻辑错误；同时更新主键前要校验$_POST['Code']的值，不能和classroom表现有code_class主键重复，主键重复也会触发约束报错。

内容的提问来源于stack exchange，提问作者Oumnia Rana SEGUENI