How to return results of a get_posts() in explicitly defined order

Okay, I was determined to find a way to do this, and I think I’ve got it. I had hoped to find a simpler solution and avoid having to use a new WP_Query object, but it’s just too ingrained into how the loop works. First, we have a couple of utility functions:

// Set post menu order based on our list  
function set_include_order(&$query, $list) {
    // Map post ID to its order in the list:
    $map = array_flip($list);

    // Set menu_order according to the list     
    foreach ($query->posts as &$post) {
      if (isset($map[$post->ID])) {
        $post->menu_order = $map[$post->ID];
      }
    }  
}

// Sort posts by $post->menu_order.                                 
function menu_order_sort($a, $b) {
  if ($a->menu_order == $b->menu_order) {
    return 0;
  }
  return ($a->menu_order < $b->menu_order) ? -1 : 1;
}

These will allow us to set the menu_order property based on our own list, and then sort the posts in a query object based on that.

Here’s how we query and sort the posts:

$plist = array(21, 43, 8, 44, 12);
$args = array(
  'post_type' => 'attachment',
  'post_status' => 'any',
  'post__in' => $plist 
);

// Create a new query  
$myquery = new WP_Query($args);

// set the menu_order
set_include_order($myquery, $plist);

// and actually sort the posts in our query
usort($myquery->posts, 'menu_order_sort');

So now we have our own query object, and the $myquery->posts is sorted according to our custom menu_order_sort function. The only tricky part now, is that we must construct our loop using our custom query object:

while($myquery->have_posts()) : $myquery->the_post();
  ?>
    <div><a id="post_id_<?php the_ID(); ?>" class="nb" href="https://wordpress.stackexchange.com/questions/11055/<?php the_permalink(); ?>"><?php the_title(); ?></a> Post ID: <?php the_ID(); ?>
    </div>
  <?php

endwhile;
wp_reset_postdata();

Obviously, you’d fix up the loop template code there.

I was hoping to find a solution that didn’t require the use of a custom query object, perhaps by using query_posts() and replacing the posts propery on the global $wp_query, but I just couldn’t get it to work right. With a little more time to work on it, that might have been doable.

Anyhow, see if that will get you where you need to go?