hibernate 删除外键约束

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hibernate 删除外键约束5

写了两个类：        Subject(一端) Comment(多端)
其对应hbm xml(截取)为：
subject.hbm.xml:
        <set
            name="comments"
            lazy="true"
            inverse="true"
            cascade="all"
            sort="unsorted"
        >
            <cache
                usage="read-write"
             />

              <key
                  column="subjectid"
              />

              <one-to-many
                  class="com.module.Comment"
              />
        </set>
//***************************************
comment.hbm.xml:

       <many-to-one
            name="subject"
            class="com.module.Subject"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="subjectid"
        />
问题：当删除subject时提示：
- SQL Error: 1451, SQLState: 23000
- Duplicate key or integrity constraint violation, message from server: "Cannot delete or update a parent row: a foreign key constraint fails (`lnc/t_comment`, CONSTRAINT `FKF437E194F69C747` FOREIGN KEY (`subjectid`) REFERENCES `t_subject` (`id`))"
- Could not synchronize database state with session
org.springframework.dao.DataIntegrityViolationException: Hibernate operation: could not delete: [com.module.Subject#32769]; SQL []; Duplicate key or integrity constraint violation, message from server: "Cannot delete or update a parent row: a foreign key constraint fails (`lnc/t_comment`, CONSTRAINT `FKF437E194F69C747` FOREIGN KEY (`subjectid`) REFERENCES `t_subject` (`id`))"; nested exception is java.sql.SQLException: Duplicate key or integrity constraint violation, message from server: "Cannot delete or update a parent row: a foreign key constraint fails (`lnc/t_comment`, CONSTRAINT `FKF437E194F69C747` FOREIGN KEY (`subjectid`) REFERENCES `t_subject` (`id`))"
java.sql.SQLException: Duplicate key or integrity constraint violation, message from server: "Cannot delete or update a parent row: a foreign key constraint fails (`lnc/t_comment`, CONSTRAINT `FKF437E194F69C747` FOREIGN KEY (`subjectid`) REFERENCES `t_subject` (`id`))"
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:1977)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1163)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1272)
at com.mysql.jdbc.Connection.execSQL(Connection.java:2236)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1741)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1588)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:105)
at net.sf.hibernate.impl.NonBatchingBatcher.addToBatch(NonBatchingBatcher.java:22)
at net.sf.hibernate.persister.EntityPersister.delete(EntityPersister.java:581)
at net.sf.hibernate.impl.ScheduledDeletion.execute(ScheduledDeletion.java:29)
at net.sf.hibernate.impl.SessionImpl.execute(SessionImpl.java:2449)
at net.sf.hibernate.impl.SessionImpl.executeAll(SessionImpl.java:2435)
at net.sf.hibernate.impl.SessionImpl.execute(SessionImpl.java:2397)
at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2261)
请碰到过这个问题的朋友帮我看看(inverse="false" 时可以删除‘一端’，但我想把维护交给‘多端‘Comment)？

问题补充：

mrliang 写道

你要删除的subject是一端而不是多端啊，当然会外键冲突了。

的确是这样，所以我想在删除 '一端'之前把与之有关联的'多端'记录先删掉或设置外键subjectid = null，按道理这样在去删 '一端'是没有就问题的，但当执行到删除'一端'时又出现异常(此时其对应的多端记录在程序里已经执行了remove，但刷新数据库记录依然健在)，大致意思是说两个不同的对象实例想用了同一个session id，我想可不可在'多端'和'一端'的删除之间做一个session 清理什么的，这样应该就能与数据库同步？

Hibernate