Custom Taxonomy List with Children

Question

I am trying to display a list of terms for a custom taxonomy and am having a bit of trouble. The custom tax is for a Custom Post Type called project.

What I want to do is list a Parent term and it's children, such as:

• Painting
  • 2013
  • 2012
  • 2011

When you get to an archive of a child term, the same list would appear, showing the parent term.

I have attempted to use wp_list_categories() and it has potential but I am not sure how to manipulate it for these purposes, meaning that when the archive is for a child term, the parent term and all other child terms are not displayed.

The code I have in the template isn't working at all, and it comes from a WP Codex example. Here is the template code:

  global $wp_query;
  $term = $wp_query->get_queried_object();
  $title = $term->name;                     
  $termID = $term->term_id;
  $taxonomy_name = $term->taxonomy;
  $termChildren = get_term_children( $termID, $taxonomy_name );

  echo $title;
  echo $termChildren;

  echo '<ul>';

  foreach ( $termChildren as $termChild ) {
    $term2 = get_term_by( 'id', $termChild, $taxonomy_name );
    echo '<li><a href="' . get_term_link( $term2->name, $taxonomy_name ) . '">' . $term2->name . '</a></li>';
  }

  echo '</ul>';

This does not render a list, and breaks everything underneath the foreach statement.

Just for good measure, here is the Custom Tax code in case I did anything stupid there:

add_action( 'init', 'register_taxonomy_mediums' );

function register_taxonomy_mediums() {

    $labels = array( 
        'name' => _x( 'Mediums', 'mediums' ),
        'singular_name' => _x( 'Medium', 'mediums' ),
        'search_items' => _x( 'Search Mediums', 'mediums' ),
        'popular_items' => _x( 'Popular Mediums', 'mediums' ),
        'all_items' => _x( 'All Mediums', 'mediums' ),
        'parent_item' => _x( 'Parent Medium', 'mediums' ),
        'parent_item_colon' => _x( 'Parent Medium:', 'mediums' ),
        'edit_item' => _x( 'Edit Medium', 'mediums' ),
        'update_item' => _x( 'Update Medium', 'mediums' ),
        'add_new_item' => _x( 'Add New Medium', 'mediums' ),
        'new_item_name' => _x( 'New Medium', 'mediums' ),
        'separate_items_with_commas' => _x( 'Separate mediums with commas', 'mediums' ),
        'add_or_remove_items' => _x( 'Add or remove mediums', 'mediums' ),
        'choose_from_most_used' => _x( 'Choose from the most used mediums', 'mediums' ),
        'menu_name' => _x( 'Mediums', 'mediums' ),
    );

    $args = array( 
        'labels' => $labels,
        'public' => true,
        'show_in_nav_menus' => true,
        'show_ui' => true,
        'show_tagcloud' => true,
        'show_admin_column' => true,
        'hierarchical' => true,
        'has_archive' => true,
        'rewrite' => true,
        'query_var' => true
    );

    register_taxonomy( 'mediums', array('project'), $args );
}

Any help would be great. Thanks!

Answer 1

Your code works perfectly in a custom taxonomy template file.

CASE 1

You're trying to use this code in a single page or something else and it doesn't work because the object returned from get_queried_object() isn't a taxonomy. The function get_queried_object() return the currently-queried object. So, if you need a Taxonomy Object you have to call it in a taxonomy archive page.

CASE 2

You're using this code in a taxonomy archive page. If you need to display the same list for parents and childrens you have to check if the current term is a children or a parent, because you have to call get_term_children() with the parent id as argument.

If you call get_term_children() with the current term ID on the children you'll probably get an empty list.

So check $term->parent value. This variable outputs the ID of the parent taxonomy. So if you are on the parent taxonomy, then $term->parent will echo 0 and you can call get_term_children() with the $term->term_id value. If you are on a children you have to call get_term_children() with the $term->parent value.