The Ajax GET request gives me an error 500

Question

I am a student and im currently working on a php project. When the below code is executed im getting an error 500.
project.js

$('#project[enter image description here][1]Modal').on('show.bs.modal', function (event) {
        var projectid = el.data('id');
        $.ajax({
            type:'GET',
            url: 'project.php',
            data: {'projectid':projectid},
            dataType : 'json',
            success : function(data) {
                if (data.success) {
                    var tot = data.amount+parseFloat(amount);
                    modal.find('#totalAmt').html(tot);
                }
            },
            error: function (jqXHR, exception) {
               alert(exception);
            }
        });
    });

project.php

<?php
include_once '../config.php';
if (isset($_GET['projectid'])) {
    $projectId = strip_tags($_POST['projectid']);
    $query = "SELECT SUM(amount) as sum FROM pledge WHERE project_id=$projectid";
    $amount = mysqli_query($mysqli, $query) or die(mysql_error());
    return $amount;
}
?>

Below is the config.php

<?php

$databaseHost = 'localhost';
$databaseName = 'lyceum';
$databaseUsername = 'root';
$databasePassword = 'la#3478';

$mysqli = mysqli_connect($databaseHost, $databaseUsername, $databasePassword, $databaseName);

?>

Below is the project structure,
lyceum
     js
       project.js
     project
       science_project.php
       project.php
config.php

Can anyone please help me with the error? Thank you in advance

Answer 1

Your issue here is you are attempting to return your values. PHP can't be returned like that, your Javascript and PHP are part of entirely separate callstacks. Whilst this isn't causing your 500 error, you've got other errors in here will.

At the beginning of your project.php you'll need to add header('Content-type: application/json'); Your AJAX call automatically expects JSON, and will treat any response it gets as JSON. However if you wished to use this elsewhere this may prevent errors.

Also, your $amount gives you a mysqli_result object, you'll need to use something like $values = mysqli_fetch_assoc($amount) to get the values required.

Then, instead of returning you'll need to echo json_encode($values['sum']) and if you do not want program execution to continue (like return does) you'll also need to exit() or die() after the echo.

Your die() on your $amount line also has an error and should take mysqli_error() instead mysql_error()

I also suggest looking at prepared statements to protect your queries from SQL injection here: https://www.w3schools.com/php/php_mysql_prepared_statements.asp

Avoid posting your database details. You never know how long your project, or this question will be around for. If your database is used for something publicly used, and you store sensitive information, someone could've taken this password a long time ago and could get write access to it.

Answer 2

To make project.js work your project.php should look like

include_once '../config.php';
if (isset($_GET['projectid'])) {
    $projectId = strip_tags($_POST['projectid']);
    $query = "SELECT SUM(amount) as sum FROM pledge WHERE project_id=$projectid";
    $amount = mysqli_query($mysqli, $query) or die(mysql_error());

    $response = array();
    $response["success"] = TRUE;
    $response["amount"] = $amount;

    echo json_encode($response);
}

Answer 3

The 500 (internal server error) means something went wrong on the server's side.

It could be several things you have to check,

1)I would start by verifying that the URL and parameters are correct. Also, make sure that whatever handles the request is expecting the request as a GET and not a POST.

2) One useful way to learn more about what's going on is to use a tool like Fiddler which will let you watch all HTTP requests and responses.

If you don't have a compelling reason to write your own Ajax code, you would be far better off using a library that handles the Ajax interactions for you. jQuery is one option.