嘿，我在媒体库中使用ACF，想按元键（实际上是由ACF创建的）对媒体进行排序。但它不起作用。

代码如下：

$gallery_imgs = get_posts(array(
    \'post_type\'         => \'attachment\',
    \'posts_per_page\'    => -1,
    \'post_mime_type\'    => \'image\',
    \'post_status\'       => \'inherit\',
    \'meta_key\'      => \'serial_no\',
    \'orderby\'       => \'meta_value\', //or \'meta_value_num\'
    \'order\'         => \'ASC\',
    \'tax_query\'         => array(
        array(
            \'taxonomy\'  => \'gallery_ct_artist_cat\',
            \'field\'     => \'term_id\',
            \'terms\'     => $artist_id
         )
    )
));