Want Page Descendants when using query_posts post_parent or child_of

Question

I'm trying to use query_posts to list all descendants of a page ID. Using post_parent only lists the first-level children.

This Trac ticket seems to address it: http://core.trac.wordpress.org/ticket/5742, but I don't understand it -- post_parent only lists the first-level children.

<?php
    query_posts( array(
    'post_parent' => 58, // Only shows posts that are direct children of the Machinery page. I want all descendants.
    //'child_of' => 58, // When used, shows posts filterd by taxonomy and term, but not filtered by child of ID 58. Acutally omits direct child of 58 but shows grandchild.
    'post_status' => 'any',
    'post_type' => 'any',
    'taxonomy' => 'industries',
    'term' => 'dairy'
    )); 
?>
<?php if ( have_posts() ) : ?>
    <h4>Dairy Machinery</h4>
    <ul>
        <?php while (have_posts()) : the_post(); ?>    
            <li>
                <a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
            </li>
        <?php endwhile; ?>
    </ul>
<?php endif; wp_reset_query(); ?>

How do I get query_posts to list all descendants of a page ID?

Answer 1

If you don't have to use query_posts() then this is one method:

function my_menu() {
    global $post;

    if(!$post->post_parent){
        // will display the subpages of this top level page
        $children = wp_list_pages( array( 'title_li' => '', 'child_of' => $post->ID, 'echo' => 0 ) );
    } elseif($post->ancestors){
        // diplays only the subpages of parent level
        $ancestors = end($post->ancestors);
        $children = wp_list_pages( array( 'title_li' => '', 'child_of' => $ancestors, 'echo' => 0 ) );
    } else {
        // diplays all pages
        $children = wp_list_pages( array( 'title_li' => '', 'echo' => 0 ) );
    }

    if ($children) {
        echo '<ul id="my-menu">';
        echo $children;
        echo '</ul>';
    }

}