Word­Press lacks one key fea­ture for advanced devel­op­ers using it as a CMS plat­form. That fea­ture is the is_child() (or would be) func­tion. If your famil­iar with Word­Press Theme Devel­op­ment you have prob­a­bly ran into the fol­low­ing Con­di­tional Tags from time to time:

• is_home()
• is_front_page()
• is_single()
• is_sticky()
• is_page()

If you ever want to have a side­bar nav­i­ga­tion dis­play the next level of child pages, you would need is_child() to do so.

// is_child()
function is_child($parent) {
	global $wp_query;
	if ($wp_query->post->post_parent == $parent) {
		$return = true;
	}
	else {
		$return = false;
	}
	return $return;
}

Usage

To use the con­di­tional in your theme(s), add the code above to functions.php. This only takes the Post IDas an argu­ment, so you’ll need to use some­thing like is_child(201); because is_child(‘Services’); will not work.

Work­ing Example

The inner Ser­vices pages on kevinleary.net use this func­tion to cre­ate a dynamic bread­crumb. I know there are plu­g­ins for this but I was look­ing for some­thing sim­ple and quick.

<?php if(is_child(221)) { ?>
		<h1 class="post-title"><a href="/services/">Services</a> <em>&gt;</em> <?php the_title(); ?></h1>
<?php } else { ?>
		<h1 class="post-title"><?php the_title(); ?></h1>
<?php } ?>

Spe­cial thanks goes out to Nicholas Rous­sos for cre­at­ing this won­der­ful gem.

is_ancestor() func­tion for deeper functionality

<?php
function is_ancestor($post_id) {
	global $wp_query;
	$ancestors = $wp_query->post->ancestors;
	if ( in_array($post_id, $ancestors) ) {
		$return = true;
	} else {
		$return = false;
	}
	return $return;
}
?>

By pop­u­lar demand, I’ve added a more in depth way to check if a post is a child OR an ances­tor of a spe­cific page ID. This hasn’t been tested yet, if it doesn’t work let me know and I can fix it.