从WordPress DB检查元值不适用于页面

I want that a CPT (Portfolio) gets created when a user is selecting a certain page template.

Here is the code I have so far, that works with posts:

$posts_with_meta = get_posts(array(
    'posts_per_page' => 1,
    'meta_key' => '_wp_page_template',
    'meta_value' => 'portfolio.php',
    'fields' => 'ids',
));

if (count($posts_with_meta)) {
    function spx_pt_portfolio()
    {
        register_post_type('portfolio',
            array(
                'labels' => array(
                    'name' => __('Portfolio'),
                    'singular_name' => __('Portfolio'),
                ),
                'public' => true,
                'has_archive' => true,
                'supports' => array('title', 'editor', 'thumbnail', 'custom-fields', 'revisions'),
            )
        );
    }

    add_action('init', 'spx_pt_portfolio');
}

For some reason, this code only works with posts. When I select the page template "Portfolio" on a page, nothing happens.

Not sure I understand exactly what you are trying to do but it might be taht you are using get_posts() and need to be using get_pages() on a page.