Subquery in ZF2 in AbstractTableGateway implementation

gistfile1.php

    public function fetchAllWithVotes()
    {
        $resultset = $this->select( function( Select $select ){

            $sub    = new Select( 'votes' );
            $sub->columns( array( 'total' => new Expression('COUNT(*)') ) )
                    ->where( 'songs.id = votes.song_id' );

            $select->columns(
                array(
                    'id',
                    'title',
                    'ytlink',
                    'votes' => new Expression( '?', array( $sub_query ) ),
                )
            );
        });
    }