ターム分割 (WordPress 4.2)

/**
 * Update featured_tags option when a shared term gets split.
 *
 * @param int    $term_id          ID of the formerly shared term.
 * @param int    $new_term_id      ID of the new term created for the $term_taxonomy_id.
 * @param int    $term_taxonomy_id ID for the term_taxonomy row affected by the split.
 * @param string $taxonomy         Taxonomy for the split term.
 */
function wporg_featured_tags_split( int $term_id, int $new_term_id, int $term_taxonomy_id, string $taxonomy ): void {
  // we only care about tags, so we'll first verify that the taxonomy is post_tag.
  if ( 'post_tag' === $taxonomy ) {

    // get the currently featured tags.
    $featured_tags = get_option( 'featured_tags' );

    // if the updated term is in the array, note the array key.
    $found_term = array_search( $term_id, $featured_tags, true );
    if ( false !== $found_term ) {

      // the updated term is a featured tag! replace it in the array, save the new array.
      $featured_tags[ $found_term ] = $new_term_id;
      update_option( 'featured_tags', $featured_tags );
    }
  }
}
add_action( 'split_shared_term', 'wporg_featured_tags_split', 10, 4 );

/**
 * Update related posts term ID for pages
 *
 * @param int    $term_id          ID of the formerly shared term.
 * @param int    $new_term_id      ID of the new term created for the $term_taxonomy_id.
 * @param int    $term_taxonomy_id ID for the term_taxonomy row affected by the split.
 * @param string $taxonomy         Taxonomy for the split term.
 */
function wporg_page_related_posts_split( int $term_id, int $new_term_id, int $term_taxonomy_id, string $taxonomy ): void {
  // find all the pages where meta_value matches the old term ID.
  $page_ids = get_posts(
    array(
      'post_type'  => 'page',
      'fields'     => 'ids',
      'meta_key'   => 'meta_key',
      'meta_value' => $term_id,
    )
  );

  // if such pages exist, update the term ID for each page.
  if ( $page_ids ) {
    foreach ( $page_ids as $id ) {
      update_post_meta( $id, 'meta_key', $new_term_id, $term_id );
    }
  }
}
add_action( 'split_shared_term', 'wporg_page_related_posts_split', 10, 4 );

/**
 * Retrieve information about split terms and udpates the featured_tags option with the new term IDs.
 *
 * @return void
 */
function wporg_featured_tags_check_split() {
  $featured_tag_ids = get_option( 'featured_tags', array() );

  // check to see whether any IDs correspond to post_tag terms that have been split.
  foreach ( $featured_tag_ids as $index => $featured_tag_id ) {
    $new_term_id = wp_get_split_term( $featured_tag_id, 'post_tag' );

    if ( $new_term_id ) {
      $featured_tag_ids[ $index ] = $new_term_id;
    }
  }

  // save
  update_option( 'featured_tags', $featured_tag_ids );
}