parent 这里是你的答案。每个术语在其parent 所有物该值是一个整数值，表示其父项的项id。所有顶级术语的值均为0 这仅仅意味着这是一个顶级术语

首先，我们需要使用父项和get_the_category. 我们将跳过0 价值观一旦有了ID数组，我们将获得所有唯一的值，并将ID数组传递给tax_query 为了保存多个查询

（以下代码未经测试，需要PHP 5.4+）

function get_related_category_posts()
{
    // Check if we are on a single page, if not, return false
    if ( !is_single() )
        return false;

    // Get the current post id
    $post_id = get_queried_object_id();

    // Get the post categories
    $categories = get_the_category( $post_id );

    // Lets build our array
    // If we don\'t have categories, bail
    if ( !$categories )
        return false;

    foreach ( $categories as $category ) {
        if ( $category->parent == 0 ) {
            $term_ids[] = $category->term_id;
        } else {
            $term_ids[] = $category->parent;
            $term_ids[] = $category->term_id;
        }
    }

    // Remove duplicate values from the array
    $unique_array = array_unique( $term_ids );

    // Lets build our query
    $args = [
        \'post__not_in\' => [$post_id],
        \'posts_per_page\' => 3, // Note: showposts is depreciated in favor of posts_per_page
        \'ignore_sticky_posts\' => 1, // Note: caller_get_posts is depreciated
        \'orderby\' => \'title\',
        \'no_found_rows\' => true, // Skip pagination, makes the query faster
        \'tax_query\' => [
            [
                \'taxonomy\' => \'category\',
                \'terms\' => $unique_array,
                \'include_children\' => false,
            ],
        ],
    ];
    $q = new WP_Query( $args );
    return $q;
}

$q = get_related_category_posts();
if ( $q->have_posts() ) {
    while ( $q->have_posts() ) {
    $q->the_post();

        // Your loop

    }
    wp_reset_postdata();
}