WordPress 刪除文章時一併刪除圖片：只刪沒被其他文章使用的安全寫法

/**
 * 永久刪除文章時,一併刪除只屬於這篇文章的圖片
 * 被其他文章當特色圖片、或出現在其他文章內文裡的圖片會保留
 */
add_action( 'before_delete_post', 'ahwei_delete_post_images' );

function ahwei_delete_post_images( $post_id ) {
    $post = get_post( $post_id );

    // 只處理一般文章;要包含頁面可改成 array( 'post', 'page' )
    if ( ! $post || ! in_array( $post->post_type, array( 'post' ), true ) ) {
        return;
    }
    // 自動草稿不處理
    if ( 'auto-draft' === $post->post_status ) {
        return;
    }

    // 候選圖片:特色圖片 + 在這篇文章上傳的圖片
    $candidates   = array();
    $thumbnail_id = (int) get_post_thumbnail_id( $post );
    if ( $thumbnail_id ) {
        $candidates[] = $thumbnail_id;
    }

    $attached = get_posts( array(
        'post_type'      => 'attachment',
        'post_status'    => 'inherit',
        'post_parent'    => $post_id,
        'post_mime_type' => 'image',
        'posts_per_page' => -1,
        'fields'         => 'ids',
    ) );

    $candidates = array_unique( array_merge( $candidates, array_map( 'intval', $attached ) ) );

    foreach ( $candidates as $attachment_id ) {
        if ( ! ahwei_is_image_used_elsewhere( $attachment_id, $post_id ) ) {
            wp_delete_attachment( $attachment_id, true );
        }
    }
}

/**
 * 檢查圖片有沒有被其他文章使用 (特色圖片或內文)
 */
function ahwei_is_image_used_elsewhere( $attachment_id, $post_id ) {
    global $wpdb;

    // 1) 是不是其他文章的特色圖片
    $as_thumbnail = (int) $wpdb->get_var( $wpdb->prepare(
        "SELECT COUNT(*) FROM {$wpdb->postmeta} pm
         INNER JOIN {$wpdb->posts} p ON p.ID = pm.post_id
         WHERE pm.meta_key = '_thumbnail_id'
           AND pm.meta_value = %s
           AND pm.post_id <> %d
           AND p.post_type <> 'revision'",
        (string) $attachment_id,
        $post_id
    ) );
    if ( $as_thumbnail > 0 ) {
        return true;
    }

    // 2) 其他文章的內文有沒有用到 (比對 wp-image-編號 與檔案路徑)
    $patterns = array( '%' . $wpdb->esc_like( 'wp-image-' . $attachment_id ) . '%' );

    $file = (string) get_post_meta( $attachment_id, '_wp_attached_file', true );
    if ( '' !== $file ) {
        // 例如 2024/05/photo-scaled.jpg 取出 2024/05/photo
        $base       = preg_replace( '/(-scaled)?\.[a-z0-9]+$/i', '', $file );
        $patterns[] = '%' . $wpdb->esc_like( $base ) . '%';
    }

    foreach ( $patterns as $like ) {
        $in_content = (int) $wpdb->get_var( $wpdb->prepare(
            "SELECT COUNT(*) FROM {$wpdb->posts}
             WHERE ID <> %d
               AND post_type NOT IN ( 'revision', 'attachment' )
               AND post_content LIKE %s",
            $post_id,
            $like
        ) );
        if ( $in_content > 0 ) {
            return true;
        }
    }

    return false;
}