Update Wordpress Custom Field with AJAX on cached page

Question

I'm new to ajax am trying to create a simple hit counter that updates a custom field in Wordpress after the page loads. The page is cached, so any attempts to use PHP alone will not work.

I'd like to simply pass the post ID through ajax to the php file, get the custom field, and update it with the new hit number.

I currently have the following code, but cannot get it to update the custom field. Here's the jquery:

 $(document).ready(function(
    $.ajax({
    url:'http://www.example.com/hits/hits.php',
    cache: false,
    type: 'POST',
    data: {PostId: '<?php echo get_the_ID() ?>'}
    });
));

And the PHP file it calls:

<?php 
/* Template Name: AJAX  */ 
?>

<?php 
    $postid = $_POST['PostId'];  // get the hits from AJAX and save it for PHP      

    $hits = (int) get_post_meta($postid, 'hit_number', true);
    $newhits = $hits + 1;
    update_post_meta($postid, 'hit_number', $newhits);
?>

What am I doing wrong? Also, is there a way to include the PHP function in the same page/file to avoid bringing in an external file? I'm concerned that as traffic gets larger, the file will be requested too often.

Thanks for your help!

Answer 1

1. WordPress loads jQuery in NoConflict mode. Do not use $. Use jQuery or one of the other solutions in the Codex.
2. If that Javascript is in a .js file, that is not going to work. You cannot run PHP in a Javascript file like that, without reconfiguring the server, and the call to get_the_ID would likely fail anyway.
3. You are directly loading a .php file. That means that WordPress is not being loaded so any attempt to use a WordPress function will not work.

Item #1 and #3 are definitely problems. Item #2 may or may not be.

You should be using the AJAX API for this. Your WordPress functions will be loaded and will work correctly. The examples on the AJAX API Codex page are pretty straightforward. It should not be hard to translate your code to that pattern, but if you have trouble I will edit the answer when I have time.