wpdb::set_blog_id PHP Method

    public function set_blog_id($blog_id, $site_id = 0)
    {
        if (!empty($site_id)) {
            $this->siteid = $site_id;
        }
        $old_blog_id = $this->blogid;
        $this->blogid = $blog_id;
        $this->prefix = $this->get_blog_prefix();
        foreach ($this->tables('blog') as $table => $prefixed_table) {
            $this->{$table} = $prefixed_table;
        }
        foreach ($this->tables('old') as $table => $prefixed_table) {
            $this->{$table} = $prefixed_table;
        }
        return $old_blog_id;
    }

 /**
  * Sets blog id.
  *
  * @since 3.0.0
  * @access public
  * @param int $blog_id
  * @param int $site_id Optional.
  * @return string previous blog id
  */
 function set_blog_id($blog_id, $site_id = 0)
 {
     $this->fields_map = new Fields_map($blog_id);
     return parent::set_blog_id($blog_id, $site_id);
 }