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->add('regions', null, [
                'choices' => isset($this->entity) ? $this->entity->getRegions() : [] ,
                'required' => false
            ])
->addEventListener(FormEvents::PRE_SUBMIT, function(FormEvent $event) {
                $data = $event->getData();
                $form = $event->getForm();

                if(!empty($data['regions'])) {

                    $regionsCollection = new ArrayCollection();
                    foreach($data['regions'] as $region) {
                        $regionsCollection->add($this->em->getRepository('AppBundle:Region')->find($region));
                    }

                     $form->add('regions', null, [
                         'data' => $regionsCollection
                     ]);
                }

  });