Make *ALL* Wordpress Categories use their Parent Category Template

Question

I want to change the default template hierarchy behavior, and force all subcategory level pages that don\'t have their own category template file to refer to their parent ca

Answer 1

/**
 * Iterate up current category hierarchy until a template is found.
 * 
 * @link http://stackoverflow.com/a/3120150/247223
 */ 
function so_3119961_load_cat_parent_template( $template ) {
    if ( basename( $template ) === 'category.php' ) { // No custom template for this specific term, let's find it's parent
        $term = get_queried_object();

        while ( $term->parent ) {
            $term = get_category( $term->parent );

            if ( ! $term || is_wp_error( $term ) )
                break; // No valid parent

            if ( $_template = locate_template( "category-{$term->slug}.php" ) ) {
                // Found ya! Let's override $template and get outta here
                $template = $_template;
                break;
            }
        }
    }

    return $template;
}

add_filter( 'category_template', 'so_3119961_load_cat_parent_template' );

This loops up the parent hierarchy until an immediate template is found.