Wordpress：投稿と一緒に使われている画像も削除する

function.phpに記入します

add_action( 'before_delete_post', 'delete_post_attachment' );
function delete_post_attachment( $post_id ) {
  $args = array(
    'numberposts' => -1,
    'post_parent' => $post_id,
    'post_type' => 'attachment',
    'post_status' => 'any',
    'post_mime_type' => 'image'
  );
  $attachments = get_children( $args );
  foreach( $attachments as $attachment ) {
     wp_delete_attachment( $attachment->ID, true );
  }
}