表外鍵在SQL語句中的取法

 有兩張表（question、answer），它們存在著一對多關聯性（question->answer）和多對一關聯性（answer->question）。

在Answer.java中定義有：
public class Answer {
    private String userid;
    private Question question;
    private int qid;
}

在answer.hbm.xml中有：
 <many-to-one name="question" class="org.lxh.myzngt.vo.Question" fetch="select">
            <column name="qid" />
 </many-to-one>

所以SQL語句如下：

public List queryByUserAnswer(String userid, int currentPage, int lineSize) {
        List all = null;
        String hql = "from Question as q where q.qid in(select a.question.qid from Answer as a where a.userid=?)";
        Query q = super.getSession().createQuery(hql);
        q.setString(0, userid);
        // 分頁操作。
        q.setFirstResult((currentPage - 1) * lineSize);
        q.setMaxResults(lineSize);        all = q.list();
        return all;
    }

否則報錯：

org.hibernate.QueryException: could not resolve property: qid of: org.lxh.myzngt.vo.Answer [select count(q.qid) from org.lxh.myzngt.vo.Question as q where q.qid in(select a.qid from org.lxh.myzngt.vo.
Answer as a where a.userid=?)]