public function freez(Registry $doctrine)
    {
        $em = $doctrine->getManager();
        // create reference to existing entity
        if ($this->country) {
            $this->country = $em->getReference(get_class($this->country), $this->country->getId());
        }
        if ($this->storage) {
            $this->storage = $em->getReference(get_class($this->storage), $this->storage->getId());
        }
        $this->type = $em->getReference(get_class($this->type), $this->type->getId());
        foreach ($this->genres as $key => $genre) {
            $this->genres[$key] = $em->getReference(get_class($genre), $genre->getId());
        }

        return $this;
    }