hibernate中如果一个字段即是主键又是外键，怎么写XML

one-to-one映射.
Hibernate的文档里面都有.
<class name="person" table="PERSON">
    <id name="id" column="PERSON_ID">
        <generator class="foreign">
            <param name="property">employee</param>
        </generator>
    </id>
    ...
    <one-to-one name="employee"
        class="Employee"
        constrained="true"/>
</class>