public function addIsActiveFilter($date = null)
    {
        $this->addFieldToFilter('is_active', true);

        if ($date == null) {
            $date = $this->date->date('Y-m-d');
        }

        $this->getSelect()
            ->where('from_date is null or from_date <= ?', $date)
            ->where('to_date is null or to_date >= ?', $date);

        return $this;
    }