Don’t customize WP, write a plugin!

Scripts and Style wrote a short post about adding a custom XML tag to your Atom feed. Unfortunately, they took the wrong route, and decided to change feed-atom.php, the file that serves up the Atom feed for a blog.

This is not at ALL necessary. The right way of doing stuff like this is writing a plugin that takes care of it, so nothing breaks when you upgrade. If you look a bit further down the code of feed-atom.php, you'll see this line of code:

<?php do_action('atom_entry'); ?>

This line of code shows that there's a so called "hook" to which you can attach an action. You attach an action to this particular hook by writing the following code:

add_action('atom_entry','add_directurl');

The first variable is the hook, the second is the function you want to call to perform your desired action. The desired action in this case was adding this line of code:

<directurl><?php echo get_post_meta($post->ID,'Author Webpage',1); ?></directurl>

So we have to write a small function that does this:

function add_directurl() {
	echo '<directurl>';
	echo get_post_meta($post->ID,'Author Webpage',1);
	echo '</directurl>';
}

Of course that could be a one liner too but that wouldn't be readable here. Now we wrap those two small blocks of code together, and add the default plugin "head" to it, and we've got ourselves a new plugin:

<?php
/*
Plugin Name: Add Direct URL to Atom Feed
Version: 0.1
Plugin URI: http://yoast.com/wordpress/
Description: Adding custom "DirectURL" tag to Atom feeds.
Author: Joost de Valk
Author URI: http://yoast.com/
*/

function add_directurl() {
	echo '<directurl>';
	echo get_post_meta($post->ID,'Author Webpage',1);
	echo '</directurl>';
}

add_action('atom_entry','add_directurl',10,1);
?>

Now, when you upgrade, you won't have to change anything, and you can safely assume that everything will keep working!