Inpsyde\MultilingualPress\API\WPDBSiteRelations::insert_relations PHP Method

    public function insert_relations($base_site_id, array $site_ids)
    {
        // We don't want to relate a site with itself.
        $site_ids = array_diff($site_ids, [$base_site_id]);
        if (!$site_ids) {
            return 0;
        }
        $values = array_map(function ($site_id) use($base_site_id) {
            return $this->get_value_pair($base_site_id, $site_id);
        }, $site_ids);
        if (!$values) {
            return 0;
        }
        $values = join(',', $values);
        return (int) $this->db->query("INSERT IGNORE INTO {$this->table} (site_1, site_2) VALUES {$values}");
    }