Wordpress search WP_Query to cover multiple post types and their custom fields?

Question

I am trying to make the WP default search a bit more intelligent, by having it use custom fields. It searches through my custom post types, but only for the usual fields (excerpt, title, content).

In my arguments to WP_Query I specify all the post types. But not sure how to specify precisely all the custom fields with an OR because I am essentially looking for content in every post type.

The code below doesn't work, gives 0 results for the keyword quality for example. But a direct search in MySQL on the wp_postmeta table suggests there are 12 posts with the word quality in it. I want my query to bring out all of them.

What's the right way to include them in the WP_Query?

1. No filters / actions
2. No plugins I'd like to do this directly in WP_Query for now, and it needs to support two languages. I'll only ever need to query one language in each search engine (PolyLang).

The code:

$SEARCH = $_GET['s']; 

$args = array(
's' => $SEARCH
,'orderby' => 'relevance'
,'post_type' => array('page', 'services', 'resources', 'events', 'reports', 'posts')
,'post_status' => 'publish'
,'posts_per_page' => 15

,'meta_query' => array(
'relation' => 'OR'

// SEARCH THROUGH "reports" post type's custom fields
,array(
    'key'   => 'report_content',
    'value' => "$SEARCH",
    'compare' => 'LIKE'
    )
,array(
    'key'   => 'report_details',
    'value' => "$SEARCH",
    'compare' => 'LIKE'
    )

 // SEARCH THROUGH "events" post type's custom fields 
,array(
    'key'   => 'event_brief',
    'value' => "$SEARCH",
    'compare' => 'LIKE'
        )
    
)

);

What I am trying to do above is to look for the word in the variable $SEARCH inside those custom fields.

EDIT: Just to add, individually separate queries work. But instead of calling WP_Query three times, I'd like to combine them into one. I have checked through dozens of "I want to combine meta_query and tax_query" posts on Stack Overflow, but none of seem to be about combining different post_types in an OR condition, as one needs in a search through a website. The three that work individually:

//MAIN QUERY
$args = array(
      's' => $SEARCH
     ,'orderby' => 'relevance'
     ,'post_type' => array('page', 'services', 'resources', 'events', 'reports', 'posts')
     ,'post_status' => 'publish'
     ,'posts_per_page' => 15
);


// SEARCH THROUGH REPORTS
$args2 = array(
          'post_type'  => 'reports'
          ,'meta_query' => array(
              'relation' => 'OR',
              array(
                      'key' => 'report_content',
                      'value' => "$SEARCH",
                      'compare' => 'LIKE',
              ),
              array(
                      'key' => 'report_details',
                      'value' => "$SEARCH",
                      'compare' => 'LIKE',
              ),
          ),
      );

// SEARCH THROUGH EVENTS
$args3 = array(
            'post_type'  => 'events'
            ,'meta_query' => array(
                'relation' => 'OR',
                array(
                        'key' => 'event_brief',
                        'value' => "$SEARCH",
                        'compare' => 'LIKE',
                ),
                array(
                        'key' => 'event_instruction',
                        'value' => "$SEARCH",
                        'compare' => 'LIKE',
                ),
            ),
          );

But combining them this kludgish way:

$wp_query       = new WP_Query( $args);
$wp_query2      = new WP_Query( $args2);
$wp_query3      = new WP_Query( $args3);

$posts          = $wp_query->posts;
$posts2         = $wp_query2->posts;
$posts3         = $wp_query3->posts;

$posts          = array_unique( array_merge(
                    $posts
                    ,$posts2
                    ,$posts3
                    ) );
                    
                    

Does not work. Gives the dreaded error:

Uncaught Error: Object of class WP_Post could not be converted to string

Anyway, I'd like to merge these meta_query with an OR condition between them. I've found multiple meta_query examples, but they presume AND... as in all those meta_queries should be matched. That's not what I want. Many thanks.

Answer 1

Found a way to combine WP_Query posts:

$query1 = new WP_Query($args);
$query2 = new WP_Query($args2);
$query3 = new WP_Query($args3);

$combined = new WP_Query();

$combined->posts =   array_merge(
                           $query1->posts
                          ,$query2->posts
                          ,$query3->posts
                        );

Still not as elegant as doing one WP_Query with all those conditions in args being an OR ... as in the query should match ANY of those meta_query options.

Also, somewhow array_unique() wrapper to the array_merge() throws an error.