ACF Custom Field WP_Query, but need to get all posts, if field doesn't exist

Question

I have a custom ACF field set on all posts, called event_date, I would like to grab all posts within a given category, but have posts that have event_date defined put first in DESC order of event_date. The args I'm using for query_posts are as follows:

$args = array(
    'posts_per_page' => -1,
    'cat' => $category_id,
    'meta_query' => array(
        array(
            'key' => 'event_date',
            'value' => date("Ymd", time()),
            'compare' => $type == 'upcoming' ? '>=' : '<'
        )
    ),
    'orderby' => 'meta_value',
    'order' => 'DESC',
    'meta_key' => 'event_date'
);

But the problem I'm facing is that the ACF field was created for post types, after all posts have been created, so many of these posts do not have event_date even defined for the meta_key (which omits these posts from the query automatically when using query_posts($args). There are too many posts to go through all posts and save them all manually, would take forever.

Basically, if the meta_key for any post does not have event_date than I need to use the date of the actual post itself (when it was published) to order by. I need all posts with event_date shown first in DESC order of event_date, than all posts that don't have event_date defined, need to be shown after that using the published date of the post in DESC order. How can I do this? Preferably, all in 1 query_posts call?

Thanks :)

Answer 1

You can get both with an OR meta_query that also checks if the key does not exist:

'meta_query' => array(
    'relation' => 'OR',
    array(
        'key' => 'event_date',
        'compare' => 'NOT EXISTS',
    ),
    array(
        'key' => 'event_date',
        'value' => date("Ymd", time()),
        'compare' => '>',
    ),
),
'orderby' => array(
    'meta_value_num' => 'DESC',
    'date' => 'ASC',
),

Answer 2

The most probable route I will take with this is to run a script that would add the desired custom field to the posts which does not have the custom field assigned.

You can try the following: (NOTE: This is untested)

add_action( 'wp', function ()
{
    $args = [
        'post_type'        => 'post', // Set according to needs
        'posts_per_page'   => -1, // Set to execute smaller chucks per page load if necessary
        'suppress_filters' => true,
        'fields'           => 'ids',
        'meta_query'       => [
            [
                'key'      => 'event_date',
                'compare'  => 'NOT EXISTS'
            ]
        ]
    ];
    $q = get_posts( $args );
    foreach ( $q as $post_id ) {
        add_post_meta( 
            $post_id, // Post ID
            'event_date', // Custom field name
            get_the_date( 'Ymd', $post_id )
        );  
     }
});

You can run this by simply loading any page after which you can remove it. If you set smaller chuncks, like posts_per_page=100, you will refresh the page until all posts are done. Note that this is quite an expensive resource intensve script which might lead to a time out fatal error, so if you have a huge amount of posts you can run smaller amount of posts per page load.

After this you can run your query as normal as per question. Just a tip though, never ever use query_posts, use WP_Query to run your custom query (or use get_posts alternatively)