when I click delete it will display this error? - php

Question

Here is the sql error
SQL error: Cannot delete or update a parent row: a foreign key constraint fails (`motioncenter`.`news`, CONSTRAINT `news_ibfk_2` FOREIGN KEY (`fk_categories_id`) REFERENCES `categories` (`category_id`))
Line: 36
Fil: C:\Xampp\htdocs\xampp\site\admin\page_functions\category_delete.php
herre is the category_delete.php file
Line: 36 is echo format_error_message(mysqli_error($database_link), $query, LINE, FILE);
<?php
if ( !isset($database_link))
{
die(header('location: index.php?page=categories'));
}
if ( !isset($_GET['category_id']))
{
die(header('location: index.php?page=categories'));
}
$category_id = ($_GET['category_id'] * 1);
$query = "DELETE FROM categories WHERE category_id = $category_id";
if (mysqli_query($database_link, $query))
{
$_SESSION['message'] .= 'deleted<br />';
die(header('location: index.php?page=categories'));
}
else
{
echo format_error_message(mysqli_error($database_link), $query, __LINE__, __FILE__);
}
?>

Answer 1

Probably your constraint that links items to category prevents you from deleting a category, while some items, news in your example, are still referencing it. Perhaps you should modify your foreign key constraint so that it does cascade delete, like ON DELETE CASCADE

Answer 2

Your database contains foreign keys that have been configured such that you cannot delete categories if there are any news items in that category.
It's kind of like trying to rm a directory that has files in it, you'll get an error saying the directory is not empty.
Add a query to "DELETE FROM news WHERE category_id=".$category_id or update the news items to be in a different category before deleting the category itself.

Answer 3

Deleting a category_id from the category table leads to an error since category_id acts a foreign key in another table. By deleting a value in category_id, all the other instances of that value in other table that reference it will be invalid.

Answer 4

You need to first delete tables with a foreign key referenced to your categories table.
motioncenter.news table has fk_categories_id field with the value you are trying to delete. you need to either delete that row in news table first or use below sql statement to disable foreign checks alltogether.
SET FOREIGN_KEY_CHECKS=0;

Answer 5

First you've to delete all news which is dependent on that category.
Then you can delete that category.
Or alternatively you can change constraint for foreign key:
# Table `motioncenter`.`news`
ALTER TABLE `motioncenter`.`news`
DROP FOREIGN KEY `news_ibfk_2`,
ADD CONSTRAINT `news_ibfk_2` FOREIGN KEY (`fk_categories_id`)
REFERENCES `categories` (`category_id`) ON DELETE CASCADE
Or if you want to keep all related news even then you should change to:
# Table `motioncenter`.`news`
ALTER TABLE `motioncenter`.`news`
DROP FOREIGN KEY `news_ibfk_2`,
ADD CONSTRAINT `news_ibfk_2` FOREIGN KEY (`fk_categories_id`)
REFERENCES `categories` (`category_id`) ON DELETE SET NULL
Because by default foreign key prevent deletion of parent record.