如何使用PHP检查删除限制上的外键约束 [英] how can I check foreign key constrain on delete restrict using PHP

问题描述

我有两个表产品和购买.我在带有 purchase.purchase_id 列的 product.purchase_id 列中设置了一个删除限制 FK.然后，如果我尝试用FK删除product.product_id，它会显示错误，就像

I have two tables Product and purchase. I set a on delete restrict FK in product.purchase_id column with purchase.purchase_id column. Then if I try to delete product.product_id with FK, It shows error just like

A Database Error Occurred

Error Number: 1451

Cannot delete or update a parent row: a foreign key constraint fails (`another_bata`.`product_purchase_item`, CONSTRAINT `FK_product_purchase_item_1` FOREIGN KEY (`product_id`) REFERENCES `product` (`product_id`) ON UPDATE CASCADE)

delete from product where product_id='158'

Filename: C:\xampp\htdocs\rima_shoe\system\database\DB_driver.php

Line Number: 330

但是我需要一个用户友好的错误，假设您无法删除此产品列表，Beause您已经有此产品了

所以我需要在php中检查此FK，我该怎么做?

So I need to check this FK in php , How can I do this?

我的第二个问题..在某些特殊情况下，是否可以删除删除限制上已经存在的'product.product_id'?假设

My second question.. Is it possible to delete a 'product.product_id' which already exist on delete restrict FK in some special case? suppose

DELETE p,q FROM product AS p INNER JOIN purchase AS q
WHERE p.purchase_id=q.purchase_id AND q.purchase_quan=0

推荐答案

使用例外:

try {
    $db->query(...);
} catch (Exception $e) {
    echo "an error occured during query";
}

您也可以创建自己的例外来专门处理FK错误:

You can also make your own Exceptions to speciallize for FK errors:

class ForeignKeyException extends Exception {
    public function __construct($msg = 0, $code = 0) {
        parent::__construct($msg, $code);
    }
}

发生FK错误时，您抛出新的ForeignKeyException('FK failed');

try {
    $db->query(...);
} catch (ForeignKeyException $e) {
    echo "FK error";
} catch (Exception $e) {
    echo "general error";
}

更新:

mysqli已经有例外:

mysqli has exceptions already:

} catch (mysqli_sql_exception $e) {
    if ($e->getCode() == 'CODE FOR FK') {
        //...
    }
}

PHP mysqli异常: http://php.net/manual/en/class.mysqli-sql-exception.php

PHP mysqli exception: http://php.net/manual/en/class.mysqli-sql-exception.php

请参见MYSQLI错误代码: http://dev.mysql.com/doc/refman/5.6/en/error-messages-server.html

See MYSQLI error codes: http://dev.mysql.com/doc/refman/5.6/en/error-messages-server.html

另一个有用的问题:在PHP中处理外键异常

第二个问题的更新:

通过

SET foreign_key_checks = 0;
<your delete query here>
SET foreign_key_checks = 1;

这篇关于如何使用PHP检查删除限制上的外键约束的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！