Hey there, let's dig into why clicking a Topic isn't loading the corresponding onderwerpen data from your second database. I'll walk through the most common issues and fixes based on what you described.

1. Double-Check Your Second Database Connection #

First off, let's make sure you're actually connecting to the right database. It's super easy to accidentally stick with the first database connection when you need to pull data from the second one.

• Verify your connection code switches to the second DB before querying onderwerpen:

// Example: Set up separate connections for each DB
$db1_conn = new mysqli($host1, $user1, $pass1, $dbname1);
$db2_conn = new mysqli($host2, $user2, $pass2, $dbname2);

// Always check for connection errors!
if ($db2_conn->connect_error) {
    die("Oops, second DB connection failed: " . $db2_conn->connect_error);
}

2. Confirm topic_id Is Being Passed Correctly #

If the connection is good, next check that the clicked Topic's topic_id is making its way to your query logic.

For Synchronous Requests (e.g., link clicks) #

Make sure your Topic links include the topic_id as a URL parameter:

<a href="load-onderwerpen.php?topic_id=<?php echo htmlspecialchars($topic['id']); ?>">
    <?php echo htmlspecialchars($topic['name']); ?>
</a>

For Asynchronous (AJAX) Requests #

If you're using JS to load data without reloading, ensure the topic_id is captured and sent:

$('.topic-link').click(function(e) {
    e.preventDefault();
    const topicId = $(this).data('topic-id'); // Ensure your link has data-topic-id="X"
    $.ajax({
        url: 'get-onderwerpen.php',
        method: 'GET',
        data: { topic_id: topicId },
        success: function(data) {
            // Dump the returned data into your container
            $('#onderwerpen-container').html(data);
        },
        error: function(xhr) {
            console.log("Request failed: ", xhr.responseText); // Check for errors here!
        }
    });
});

3. Fix Your Database Query #

Now let's make sure your SQL query is targeting the second DB, filtering correctly, and avoiding injection risks.

// Grab the topic_id from the request (use $_POST if you're using POST)
$topic_id = $_GET['topic_id'] ?? null;

if (!$topic_id) {
    echo "No topic ID provided!";
    exit;
}

// Use the SECOND database connection ($db2_conn) here!
$stmt = $db2_conn->prepare("SELECT * FROM onderwerpen WHERE topic_id = ?");
$stmt->bind_param("i", $topic_id); // "i" = integer, adjust if your topic_id is a string
$stmt->execute();
$result = $stmt->get_result();

// Render the results
if ($result->num_rows > 0) {
    while ($item = $result->fetch_assoc()) {
        echo "<div class='onderwerp-item'>" . htmlspecialchars($item['name']) . "</div>";
        // Add other fields you need to display
    }
} else {
    echo "No onderwerpen found for this topic.";
}

// Clean up
$stmt->close();
$db2_conn->close();

4. Debug Frontend Rendering #

If your backend is returning the right data but nothing shows up, check these:

• Open your browser's DevTools (F12) → Console tab: Look for JS errors that might be blocking rendering.
• Go to the Network tab: Check if the request to load onderwerpen succeeds, and verify the response has the data you expect.
• Make sure you're inserting the returned data into the correct DOM element (e.g., #onderwerpen-container exists on your page).

Quick Debugging Checklist #

1. Run your SQL query directly in the second database (e.g., SELECT * FROM onderwerpen WHERE topic_id = 5) to confirm data exists.
2. echo $topic_id; in your PHP script to make sure it's being received correctly.
3. Check for database errors by enabling error reporting in PHP: error_reporting(E_ALL); ini_set('display_errors', 1);

内容的提问来源于stack exchange，提问作者helpmeifyoucangg