public function prepare($builder = null)
    {
        // NOTE: because the same ActiveQuery may be used to build different SQL statements
        // (e.g. by ActiveDataProvider, one for count query, the other for row data query,
        // it is important to make sure the same ActiveQuery can be used to build SQL statements
        // multiple times.
        if (!empty($this->joinWith)) {
            $this->buildJoinWith();
            $this->joinWith = null;
        }

        return $this;
    }