Hierarchical display of custom taxonomy

Question

I'm creating a property theme and I have a hierarchical taxonomy 'property_location' registered for the custom post type 'property'. Each property will be assigned a location through this tax, which may have one or more parents in a hierarchical fashion. So for instance if I assign the location term of 'Springs' to a property, which is a child term of 'Gauteng', it should give me

Springs, Gauteng

And if Gauteng happens to be a child term of 'South Africa', it should give me

Springs, Gauteng, South Africa

But if I just assign the 'Gauteng' term (assuming it is a child term of the 'South Africa' term, it should give me

Gauteng, South Africa

So my question is how would I write a function smart enough to find the lowest level location term assigned to a property and get its parent terms in order? Is there any Wordpress functions that would help?

Answer 1

The wpse244577_list_terms() function below uses wp_list_categories() to do the heavy lifting, then modifies the results so that the terms are in reverse order of the hierarchy.

Place this code in a plugin or your theme's functions.php file:

/**
 * Lists term links for a taxonomy in reverse order of hierarchy
 * 
 * Based on https://developer.wordpress.org/reference/functions/wp_list_categories/#comment-1169    
 * @param $taxonomy string taxonomy name
 * @param $separator string separator for terms
 */
function wpse244577_list_terms( $taxonomy, $separator = ', ' ) {        

    // Get the term IDs assigned to post.
    $post_terms = wp_get_object_terms( get_the_ID(), $taxonomy, [ 'fields' => 'ids' ] );

    if ( ! empty( $post_terms ) && ! is_wp_error( $post_terms ) ) {

        $terms = wp_list_categories( [
                'title_li'  => '',
                'style'     => 'none',
                'echo'      => false,
                'taxonomy'  => $taxonomy,
                'include'   => $post_terms,
                'separator' => $separator,
        ] );

        $terms = rtrim( trim( str_replace( $separator, $separator, $terms ) ), ', ' );
        $terms = explode( $separator, $terms );
        $terms = array_reverse( $terms );
        $terms = implode( $separator, $terms );

        echo  $terms;
    }
}

To use the function, call it within the loop of your theme, passing the desired taxonomy name as the first parameter:

wpse244577_list_terms( 'property_location' );