pre_get_posts and search query for admin

I’m going round in circles with trying to include several custom fields in my search results. The custom fields are managed via ACF.

At first I want this for the admin. /wp-admin/edit.php?post_type=location.

I can’t see why this wont work. I have tried variations of it and different orders. I’ve also gone through the posts_search filter route with arrays but just can’t get this to work.

Any help appreciated.

add_filter('pre_get_posts', __NAMESPACE__ . '\\search_custom_fields');

function search_custom_fields($query)
{
if ($query->is_search && $query->is_main_query()) {
    // this works.
    echo "search_custom_fields:   " . $query->is_main_query() . " " . $query->is_search;
    echo "Setting meta_query in search_custom_fields. ";

    $search_word = get_query_var('s');

    $meta_query = array(
        'relation' => 'OR',
        array(
            'key'     => 'loc_refid',
            'value'   => get_search_query(),
            'compare' => 'LIKE',
        ), array(
            'key'     => 'location_postcode_preview',
            'value'   => get_search_query(),
            'compare' => 'LIKE',
        ),
    );

    // if i uncomment this no results appear?!
    // $query->set('meta_query', $meta_query);

    // these work have an affect on the results
    $query->set('orderby', 'date');  
    $query->set('order', 'ASC');

}

return $query;

}

print_r($query) gives me –

 [query_vars]=>
        [meta_query] => Array
                (
                    [key] => loc_refid
                    [value] => MN0068
                    [compare] => LIKE
                )

 [meta_query] =>  
 [date_query] => 
 [post_count] => 0
 ...

thanks in advance.

Have you tried it with add_action instead of add_filter ?

add_action('pre_get_posts', 'search_custom_fields');

Is public set to true for your post_type?

And for use on in admin, try:

if ( is_admin() && $query->is_main_query() ) {
    if ( $query->is_search ) {
       //etc.