Novelist: Order series archive by publication date

novelist-series-archive-orderby.php

<?php
/**
 * Modify Book Query
 *
 * Modifies the WP_Query to change the series archive "orderby" parameter to use
 * the book's publication date rather than the number in the series. This
 * eliminates the need to fill out the book series number.
 *
 * @param WP_Query $query
 *
 * @return void
 */
function ag_novelist_series_archive_orderby( $query ) {

	if ( ! $query->is_main_query() || is_admin() ) {
		return;
	}

	if ( is_tax( 'novelist-series' ) ) {
		$query->set( 'orderby', 'meta_value_num' );
		$query->set( 'order', 'ASC' );
		$query->set( 'meta_key', 'novelist_pub_date_timestamp' );
	}

}

add_action( 'pre_get_posts', 'ag_novelist_series_archive_orderby', 100 );