Error 500 When Updating MySql Database from WordPress - Same Code Works Fine Outside of WordPress-CodePudding

I need to update a MySql database from inside a JS function within a WordPress Woocommerce page. I'm using Ajax to do this. The following code works fine as a stand-alone code but when I put it into the WordPress page (on my localhost) it throws an error 500. Also I put the required data (which will eventually be a variable) onto the end of the url (?test=14230) because I couldn't get it to send the data when using the data: line in the Ajax.

Here's the Ajax:

function db()
{
   
         $.ajax({
      url: 'update_db.php?test=14230',
      type: 'post',
      data: 0,
      success: function(output) 
      {
          alert('Success, server says ' output);
      }, error: function()
      {
          alert('Something went wrong.');
      }
   });
   
}

Here's the update_db.php:

<?php
if(isset($_GET['test']) ){
$id = $_GET['test'];
}
        
    include 'database-handler.php';
    
    $sql = "UPDATE db_name SET column = 'Some Value' WHERE id = $id";

    if(mysqli_query($conn, $sql)){
        //echo ('<p>'."Success.".'</p>');
    } else {
        //echo ('<p>'."Something went wrong. $sql. " . mysqli_error($conn).'</p>');
    }
    
    mysqli_close($conn);  
?>

So I'm just wondering why this works as a stand-alone code but not when it's inside WordPress?

Edit: Here is the error log:

[Wed Nov 09 15:16:47.543162 2022] [php:error] [pid 4564:tid 1828] [client ::1:5888] PHP Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in C:\xampp\htdocs\my-sites\wowcard\wp-content\themes\blocksy-child\woocommerce\single-product\save-card-size.php:17\nStack trace:\n#0 C:\xampp\htdocs\my-sites\wowcard\wp-content\themes\blocksy-child\woocommerce\single-product\save-card-size.php(17): mysqli_query(NULL, 'UPDATE new_card...')\n#1 {main}\n thrown in C:\xampp\htdocs\my-sites\wowcard\wp-content\themes\blocksy-child\woocommerce\single-product\save-card-size.php on line 17, referer: http://localhost/my-sites/wowcard/product/polka-dot-brush-strokes-two-photo-birthday-card-purple/?card=complete&id=14230

CodePudding user response：

The error was because of this line:

include 'database-handler.php';

Replacing the include with the contents of database-handler.php fixed the issue.

CodePudding user response：

WordPress has its own database handler which is automatically loaded, there are most likely conflicts between your code and WordPress, but without seeing the actual error, I can not give more information.

Check this out https://developer.wordpress.org/reference/classes/wpdb/

Example:

global $wpdb;
$results = $wpdb->query($wpdb->prepare( 'UPDATE db_name SET column = 'Some Value' WHERE id = %d' , $id ));