Search custom post type posts only by meta fields?

Question

is it possibile to search custom post type product by _sku or other custom meta field with input text field? I don't want to use plugin, just need custom WP function.

I have found this solution for search only by title:

function __search_by_title_only($search, &$wp_query)
{
    global $wpdb;
    if (empty($search))
        return $search; // skip processing - no search term in query
    $q = $wp_query->query_vars;
    $n = !empty($q['exact']) ? '' : '%';
    $search =
        $searchand = '';
    foreach ((array) $q['search_terms'] as $term) {
        $term = esc_sql(like_escape($term));
        $search .= "{$searchand}($wpdb->posts.post_title LIKE '{$n}{$term}{$n}')";
        $searchand = ' AND ';
    }
    if (!empty($search)) {
        $search = " AND ({$search}) ";
        if (!is_user_logged_in())
            $search .= " AND ($wpdb->posts.post_password = '') ";
    }
    return $search;
}
add_filter('posts_search', '__search_by_title_only', 500, 2);

... but I need function like this for meta fields ( _sku and _author ).

Thanks !

Answer 1

This might work, not tested though. First add this to join the postmeta table:

add_filter( 'posts_join', 'search_filters_join', 501, 2 );

function search_filters_join( $join, $query ) {
    global $wpdb;

    if ( empty( $query->query_vars[ 'post_type' ] ) || $query->query_vars[ 'post_type' ] !== 'product' ) {
        return $join; // skip processing
    }

    if ( ($this->is_ajax_search() || $this->is_search_page()) && !is_admin() ) {

            $join .= " INNER JOIN $wpdb->postmeta AS customsearch ON ( $wpdb->posts.ID = customsearch.post_id )";
    }


    return $join;
}

Then modify your $search-variable in the foreach-loop as to include the following (this example shows _sku, just add on _author to another OR section if you want to search for that as well):

$search .= "{$searchand} (($wpdb->posts.post_title LIKE '{$n}{$term}{$n}') OR (customsearch.meta_key='_sku' AND customsearch.meta_value LIKE '{$n}{$term}{$n}'))";