我正在尝试连接两种自定义帖子类型。通过大量的google搜索，我发现了下面的代码，它在管理屏幕上添加了一个元框，以从另一种帖子类型中选择一篇帖子作为父级，但是如何在数据库中将该帖子设置为父级呢？

add_action(\'admin_menu\', function() {
    remove_meta_box(\'pageparentdiv\', \'episodes\', \'normal\');
});
add_action(\'add_meta_boxes\', function() {
    add_meta_box(\'episodes-parent\', \'Cartoon Series\', \'episodes_attributes_meta_box\', \'episodes\', \'side\', \'default\');
});

function episodes_attributes_meta_box($post) {
    $post_type_object = get_post_type_object($post->post_type);
    if ( $post_type_object->hierarchical ) {
        $pages = wp_dropdown_pages(array(\'post_type\' => \'cartoon-series\', \'selected\' => $post->post_parent, \'name\' => \'parent_id\', \'show_option_none\' => __(\'(no parent)\'), \'sort_column\'=> \'menu_order, post_title\', \'echo\' => 0));
        if ( ! empty($pages) ) {
            echo $pages;
        } // end empty pages check
    } // end hierarchical check.
}