您清楚地提到this function 其用法如下：

global $post;
$parents = get_post_ancestors( $post->ID );

此函数提供附件附加到的post ID列表。

粘贴此代码functions.php

/**
 * get_attachment_parent fx gives array of post id to which given attachment attach
 * @param  [int $att_id attachment id
 * @return array        list of post ids
 */
function ravs_get_attachment_parent( $att_id ){

    $args=array(
        \'posts_per_page\'  => -1,
        );

    $posts=get_posts($args);

    if( ! $posts && empty($posts) )
            return array();

    $ancestors = array();

    foreach ($posts as $post) {
        $attachment = get_post_thumbnail_id($post->ID);
        if( $att_id === $attachment  && ! in_array($post->ID, $ancestors))
            $ancestors[] = $post->ID;
    }
    return $ancestors;
}

if( has_post_thumbnail() )
 print_r( ravs_get_attachment_parent( get_post_thumbnail_id(get_the_ID())) );

print_r( ravs_get_attachment_parent( $attachment_id );