public function isValidStartDate(Campaign $campaign, \DateTime $startDate)
    {
        if($startDate != $campaign->getStartDate()){
            /*
             * While changing the campaign start date, has an earlier
             * Action been added by someone else?
             */
            /** @var Action $firstAction */
            $firstAction = $this->em->getRepository('CampaignChain\CoreBundle\Entity\Campaign')
                ->getFirstAction($campaign);

            if($firstAction && $startDate > $firstAction->getStartDate()){
                return false;
            }
        }

        return true;
    }