Query Posts that have or don't have a meta_value and order by the same ASC

Question

I'm trying to perform a scheduled update to all posts, 10 posts at time.

To achieve this, I run Cron job with a script that saves 2 post meta:

• $DATA: the data I want to be update
• $TIME: the UNIX timestamp: time(), to know when that post has been updated with a new $DATA

As I have a lot of posts that do not have the $DATA postmeta, when I query the posts to perform the update I want the posts to be ordered like this:

1. First I want any post that does not have the $TIME postmeta
2. Then all others, starting from the ones I've updated earlier

These are the query arguments I'm using:

$args = array(
   'post_type' => 'post',
   'post_status' => 'publish',
   'posts_per_page' => '10',
   'meta_query' => array(
      'relation' => 'OR',
       array( 
               'key' => 'TIME_meta_key',
               'compare' => 'EXISTS'
           ),
         array(
               'key' => 'TIME_meta_key',
               'compare' => 'NOT EXISTS',
               'value' => 'xxx'  // I've read this is a bug, so I put a value even if it's ignored
           ),
       ),
   'orderby' => 'TIME_meta_key',
   'order' => 'ASC'
 );

As I said before, the TIME_meta_key value (when exists) is just a UNIX timestamp.

So, as I want to update first the posts that are still not updated, then the ones that have been updated earlier in time, I assume I have to order ASC.

But if I set ASC, this does not work. it keep updating the posts that already have a value in the TIME_meta_key field.

Is this normal or I'm making some stupid mistake?

Answer 1

You can do this by naming index of meta query, then passing array of these names in orderby parameter

$args = array(
   'post_type' => 'post',
   'post_status' => 'publish',
   'posts_per_page' => '10',
   'meta_query' => array(
      'relation' => 'OR',
      'with_time' => array( 
               'key' => 'TIME_meta_key',
               'compare' => 'EXISTS'
           ),
      'without_time' => array(
               'key' => 'TIME_meta_key',
               'compare' => 'NOT EXISTS',
               /* 'value' => 'xxx'  The bug has been fixed ; */
           ),
       ),
   /* First order posts those does not have meta key then those have meta key in ascending order */
   'orderby' => array(
       'without_time' => 'ASC',
       'with_time' => 'ASC'
   ),
 );

In orderby array first key is without_time then with_time thus it will bring up all the posts first those does not have TIME_meta_key however, these posts will not have order (Will be default based on ID) because meta key does not exist. Then it will join the posts those have meta key TIME_meta_key in ascending order.

So the final outcome will be posts without meta key orderby ID then posts with meta key order by value ascending.

NOTE 1: these syntax are only supported since WordPress version 4.2
NOTE 2: Another bug related to NOT EXIST has been fixed in WordPress 3.9