src/Zf2Forum/Model/Message/MessageHydrator.php
public function extract($object)
    {
        if (!$object instanceof MessageInterface) {
            throw new Exception\InvalidArgumentException('$object must be an instance of Zf2Forum\Model\Message\MessageInterface');
        }
        $data = parent::extract($object);


        $thread = $object->getThread();
        $data['forum_topic_id'] = (int)$thread->getId();
        unset($data['topic']);
        $data['timestamp_created'] = $data['timestamp_created']->format('Y-m-d H:i:s');
        return $data;
    }
public function extract($object)
    {
        if (!$object instanceof MessageInterface) {
            throw new Exception\InvalidArgumentException('$object must be an instance of Zf2Forum\Model\Message\MessageInterface');
        }
        $data = parent::extract($object);


        $thread = $object->getThread();
        $data['forum_topic_id'] = (int)$thread->getId();
        unset($data['topic']);
        $data['timestamp_created'] = $data['timestamp_created']->format('Y-m-d H:i:s');
        return $data;
    }
Extract values from an object

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