[WordPress]カスタムフィールドの値も検索対象に含める

functions.php

function cf_search_join( $join ) {
  global $wpdb;
  if ( is_search() ) {
    $join .= ' LEFT JOIN ' . $wpdb->postmeta . ' ON ' . $wpdb->posts . '.ID = ' . $wpdb->postmeta . '.post_id ';
  }
  return $join;
}
add_filter( 'posts_join', 'cf_search_join' );

function cf_search_where( $where ) {
  global $wpdb;
  if ( is_search() ) {
    $where = preg_replace(
      "/\(\s*" . $wpdb->posts . ".post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
      "(" . $wpdb->posts . ".post_title LIKE $1) OR (" . $wpdb->postmeta . ".meta_value LIKE $1)", $where );

    // 特定のカスタムフィールドを検索対象から外す（※１）
//    $where .= " AND (" . $wpdb->postmeta . ".meta_key NOT LIKE 'number')";
//    $where .= " AND (" . $wpdb->postmeta . ".meta_key NOT LIKE 'zip')";
//    $where .= " AND (" . $wpdb->postmeta . ".meta_key NOT LIKE 'access')";
  }
  return $where;
}
add_filter( 'posts_where', 'cf_search_where' );

function cf_search_distinct( $where ) {
  global $wpdb;
  if ( is_search() ) {
    return "DISTINCT";
  }
  return $where;
}
add_filter( 'posts_distinct', 'cf_search_distinct' );

// 検索対象を『タイトルのみ』にする
function __search_by_title_only( $search, & $wp_query ) {
  global $wpdb;
  if ( empty( $search ) )
    return $search; // skip processing - no search term in query
  $q = $wp_query->query_vars;
  $n = !empty( $q[ 'exact' ] ) ? '' : '%';
  $search =
    $searchand = '';
  foreach ( ( array )$q[ 'search_terms' ] as $term ) {
    $term = esc_sql( like_escape( $term ) );
    $search .= "{$searchand}($wpdb->posts.post_title LIKE '{$n}{$term}{$n}')";
    $searchand = ' AND ';
  }
  if ( !empty( $search ) ) {
    $search = " AND ({$search}) ";
    if ( !is_user_logged_in() )
      $search .= " AND ($wpdb->posts.post_password = '') ";
  }
  return $search;
}