[WordPress] change next / previous post link ordering

gistfile1.php

<?php
/**
 * Customize Adjacent Post Link Order
 */
function my_custom_adjacent_post_where($sql) {
	if ( !is_main_query() || !is_singular() )
		return $sql;
	
	$the_post = get_post( get_the_ID() );
	$patterns = array();
	$patterns[] = '/post_date/';
	$patterns[] = '/\'[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2}\'/';
	$replacements = array();
	$replacements[] = 'menu_order';
	$replacements[] = $the_post->menu_order;
	return preg_replace( $patterns, $replacements, $sql );
}
add_filter( 'get_next_post_where', 'my_custom_adjacent_post_where' );
add_filter( 'get_previous_post_where', 'my_custom_adjacent_post_where' );

function my_custom_adjacent_post_sort($sql) {
	if ( !is_main_query() || !is_singular() )
		return $sql;
	
	$pattern = '/post_date/';
	$replacement = 'menu_order';
	return preg_replace( $pattern, $replacement, $sql );
}
add_filter( 'get_next_post_sort', 'my_custom_adjacent_post_sort' );
add_filter( 'get_previous_post_sort', 'my_custom_adjacent_post_sort' );

カスタム投稿タイプなどで、アーカイブ等で 'orderby' => 'menu_order' で表示しているサイトで、 previous_post_link() next_post_link() を使う方法