src/Zf2Forum/Model/Topic/TopicMapper.php
public function getTopicById($id)
    {
        $select = $this->getSelect()->where(array(
            'id' => $id
        ));
        $ret = $this->select($select)->current();
        /**
         *
         * @return \Zd2Forum\Options\ModuleOptions
         */
        $options = $this->getServiceLocator()->get('Zf2Forum\ModuleOptions');
        $funcName = "get" . $options->getUserColumn();
        $user = $this->getServiceLocator()
            ->get("Zf2Forum_user_mapper")
            ->findById($ret->getUserId());
        $ret->user = $user->$funcName();
        return $ret;
    }
public function getTopicById($id)
    {
        $select = $this->getSelect()->where(array(
            'id' => $id
        ));
        $ret = $this->select($select)->current();
        /**
         *
         * @return \Zd2Forum\Options\ModuleOptions
         */
        $options = $this->getServiceLocator()->get('Zf2Forum\ModuleOptions');
        $funcName = "get" . $options->getUserColumn();
        $user = $this->getServiceLocator()
            ->get("Zf2Forum_user_mapper")
            ->findById($ret->getUserId());
        $ret->user = $user->$funcName();
        return $ret;
    }
getTopicById

@param int $int
@return TopicInterface