java hibernate 无主键表 更新

遇到这样的问题，用hibernate 开发，myeclipse 反向生成映射文件，现有表eventAlert，此表是个没有主键的表，生成的映射文件，如下：

<hibernate-mapping>
    <class name="com.tomsync.vo.EventAlert" table="EventAlert" catalog="obm">
        <composite-id name="id" class="com.tomsync.vo.EventAlertId">
            <key-property name="eventalertTimeupdate" type="java.util.Date">
                <column name="eventalert_timeupdate" length="19" />
            </key-property>
            <key-property name="eventalertTimecreate" type="java.util.Date">
                <column name="eventalert_timecreate" length="19" />
            </key-property>
            <key-many-to-one name="userObm" class="com.tomsync.vo.UserObm">
                <column name="eventalert_userupdate" />
            </key-many-to-one>
            <key-many-to-one name="userObm_1" class="com.tomsync.vo.UserObm">
                <column name="eventalert_usercreate" />
            </key-many-to-one>
            <key-many-to-one name="event" class="com.tomsync.vo.Event">
                <column name="eventalert_event_id" />
            </key-many-to-one>
            <key-many-to-one name="userObm_2" class="com.tomsync.vo.UserObm">
                <column name="eventalert_user_id" />
            </key-many-to-one>
            <key-property name="eventalertDuration" type="java.lang.Integer">
                <column name="eventalert_duration" />
            </key-property>
        </composite-id>
        <many-to-one name="userObmByEventalertUserupdate" class="com.tomsync.vo.UserObm" update="false" insert="false" fetch="select">
            <column name="eventalert_userupdate" />
        </many-to-one>
        <many-to-one name="userObmByEventalertUserId" class="com.tomsync.vo.UserObm" update="false" insert="false" fetch="select">
            <column name="eventalert_user_id" />
        </many-to-one>
        <many-to-one name="event" class="com.tomsync.vo.Event" update="false" insert="false" fetch="select">
            <column name="eventalert_event_id" />
        </many-to-one>
        <many-to-one name="userObmByEventalertUsercreate" class="com.tomsync.vo.UserObm" update="false" insert="false" fetch="select">
            <column name="eventalert_usercreate" />
        </many-to-one>
    </class>
</hibernate-mapping>


如上，虚拟出类 com.tomsync.vo.EventAlertId  作为它的主键，在项目中，读取，没有问题，当我要对 com.tomsync.vo.EventAlertId 类中的 eventalertDuration 做更新的时候，不抱异常，项目运行一切正常，但是，库中的数据就是没有改过来。还是新建时候的数据。
请问，对于虚拟出来的主键  com.tomsync.vo.EventAlertId 类中的属性 eventalertDuration 是不是不可修改？