Getting grandchildren of a post with a specified custom taxonomy?

I was able to achieve this by, funnily enough, using with get_pages() and WP_Query(). I wanted a reusable function that would return a WP_Query array that I could loop through, so I came up with this:

function returnChildGeographies($geoID, $geoType, $grandChildren = false) {

    $args = array(
        'post_type'         => 'geographies',
        'posts_per_page'    => -1,
        'orderby'           => 'post_title',
        'order'             => 'ASC',
        'post_parent'       => $geoID,
        'tax_query'         => array(
            array(
            'taxonomy' => 'geographytype',
            'field' => 'slug',
            'terms' => $geoType
            )
        )
    );

    if ($grandChildren) {
        $getPagesArgs = array(
            'sort_order' => 'ASC',
            'sort_column' => 'post_title',
            'hierarchical' => 0,
            'child_of' => $geoID,
            'post_type' => 'geographies'
        );

        $pagesArray = get_pages($getPagesArgs);
        $grandChildArray = array();

        foreach ($pagesArray as $grandchild) {
            $grandChildArray[] = $grandchild->ID;
        }

        unset($args['post_parent']);
        $args['post__in'] = $grandChildArray;
    }

    $childArray = new WP_Query($args);

    return $childArray;
}

As an example usage: if I’m viewing the Americas area and I want to get all of the cities (which are which are grandchildren of the area), I call:

$regionQuery = returnChildGeographies($post->ID, 'city', true);

If I only want direct children:

$countryQuery = returnChildGeographies($post->ID, 'country', false);

Based on that last parameter, the function will unset post_parent and set post__in, which is an array of the post IDs I’m looking for.

The function could probably be neatened up quite a bit, but the method stands: combining get_pages() and WP_Query() seemed like the best way of getting grandchildren (or great-grandchildren, or great-great-grandchildren) and using a custom taxonomy query.

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