$events = Doctrine_Query::create()
    ->select('e.*, v.*, s.*, MIN(date_start) as v.date_start, MAX(date_finish) as v.date_finish')
    ->from('Event e')
    ->leftJoin('e.Venues v')
    ->leftJoin('v.Sessions')
    ->where('e.is_hidden = ?', false)
    ->fetchArray();