It feels good to be a part of open source project.

Many people ask on WordPress – Stack Exchange how to echo class depending on parent category, best way to do this is to use post_class filter, so I wrote small chunk of code to this.

Following code is based on Chip Bennett’s clever solution. I changed big part of it, but logic is the same.

add_filter( 'post_class', 'mamaduka_add_parent_category_class' );
/**
 * Add parent category class to post_class() function
 *
 * @link http://wordpress.stackexchange.com/q/23259#23260
 */
function mamaduka_add_parent_category_class( $classes ) {
	global $post;

	foreach ( (array) get_the_category( $post->ID ) as $cat ) {
		if ( ! empty( $cat->parent ) ) {
			$parent_cat = &get_category( $cat->parent );
			$classes[] = 'category-parent-' . sanitize_html_class( $parent_cat->slug, $parent_cat->term_id );
		} else {
			$classes[] = 'category-parent-' . sanitize_html_class( $cat->slug, $cat->term_id );
		}
	}
	return $classes;
}

What the code above does is simple, it gets array of category objects assigned to the post, then if category has parent it adds class ‘category-parent-{parent-cat-name}’, otherwise category is top-level so we are using it.

Problem: If user adds both parent and its child categories, we’ll get duplicated class output of parent category.

This is small problem I’m working now, any suggestions are welcome.

I’ve no idea about my future posts, but I think my main subject will be WordPress.