public function extract($object)
    {
        if (!$object instanceof TopicInterface) {
            throw new Exception\InvalidArgumentException('$object must be an instance of Zf2Forum\Model\Topic\TopicInterface');
        }
        $data = parent::extract($object);
        if ($data['id'] == "") {
            unset($data['id']);
        }
        unset($data['message_count']);
        unset($data['visit_count']);
        unset($data['last_post']);
        return $data;
    }
public function extract($object)
    {
        if (!$object instanceof TopicInterface) {
            throw new Exception\InvalidArgumentException('$object must be an instance of Zf2Forum\Model\Topic\TopicInterface');
        }
        $data = parent::extract($object);
        if ($data['id'] == "") {
            unset($data['id']);
        }
        unset($data['message_count']);
        unset($data['visit_count']);
        unset($data['last_post']);
        return $data;
    }
Extract values from an object

@param  object $object
@return array
@throws Exception\InvalidArgumentException