WP Query - Order by metavalue and keep other posts - php

Question

Can't figure out this problem. Goal: I want to show all posts and order them by a post meta value, but not all posts have that meta key.
Problem: Not all posts are shown, only the ones that have that meta key (and meta value).
$args = array(
'post_type' => 'post',
'meta_key' => 'post_custom_field_1',
'orderby' => 'meta_value',
'order' => 'ASC',
'paged' => $paged,'post_type' => 'post' );
Question: How can I show all posts and sort them by a meta_key? Posts that have the meta_key are shown first and ordered by name and posts that don't have the meta_key follow and are sorted by title.

Answer 1

You'll have to use EXISTS for compare. There are plenty of examples in the docs for WP_Query, you can adapt it to your case:
function orderby_fieldifexists($orderby) {
return "mt1.post_id IS NOT NULL DESC, wp_postmeta.meta_value ASC";
}
add_filter("posts_orderby", "orderby_fieldifexists", 10, 1);
$query = new WP_Query(
array(
'post_type' => 'post',
'meta_query' => array(
"relation" => "or",
'custom_field_value' => array(
'key' => 'post_custom_field_1',
),
'custom_field' => array(
'key' => 'post_custom_field_1',
'compare' => 'NOT EXISTS',
),
),
'orderby' => array(
'custom_field' => 'ASC'
),
'posts_per_page' => 5,
)
);
I've initially had a simpler version in here, but then remembered that it would be silly to sort numerically if some values will be NULL. This version will find all posts, but get the value as well, and sort descending on "does it exist?" and then ascending on the actual values, so a post with a custom field value of -1 will be listed before those without that custom field value.