hibernate多对多的更新问题

错误原因

A different object with the same identifier value was already associated with the session : [com.dabai.pojo.Privilege#2]; nested exception is org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [com.dabai.pojo.Privilege#2]] with root cause
org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [com.dabai.pojo.Privilege#2]

大意可以理解成在hibernate的更新操作时发生了主键冲突；我这里是由于多对多的关系导致的。因为Privilege和Role之间我的更新是直接 new 多个Privilege然后赋值给Role的Set，这是最根本的原因。要知道hibernate在session中判别实体是通过该实体的主键唯一性判别的。我的错误dao层方法：

public void updateRole(Role role) {
        getHibernateTemplate().update(role);
        
    }

service层方法：

public void editRole(Role role, String[] privilege_ids) {
        Set<Privilege>set=new HashSet<>();
        for (String id : privilege_ids) {
            Privilege privilege=new Privilege();
            privilege.setPrivilege_id((long) Integer.parseInt(id));
            set.add(privilege);
        }
        role.setPrivileges(set);
        roleDao.updateRole(role);

如果犯了和我相同的错误的话可以尝试使用

getHibernateTemplate().merge(role);

如果是操纵session操作的话使用

session.merge(role);

下面是hibernate的merge方法的具体实现

    @Override
    public <T> T merge(final T entity) throws DataAccessException {
        return executeWithNativeSession(new HibernateCallback<T>() {
            @Override
            @SuppressWarnings("unchecked")
            public T doInHibernate(Session session) throws HibernateException {
                checkWriteOperationAllowed(session);
                return (T) session.merge(entity);
            }
        });
    }

hibernate有关merge官方解释：

<T> T org.springframework.orm.hibernate5.HibernateTemplate.merge(T entity) throws DataAccessException


Copy the state of the given object onto the persistent objectwith the same identifier. Follows JSR-220 semantics. 

Similar to saveOrUpdate, but never associates the givenobject with the current Hibernate Session. In case of a new entity,the state will be copied over as well. 

Note that merge will not update the identifiersin the passed-in object graph (in contrast to TopLink)! Considerregistering Spring's IdTransferringMergeEventListener ifyou would like to have newly assigned ids transferred to the originalobject graph too.

　　参照某位大佬的解释：

session.merge()方法会首先发送一句select语句，去数据库端获取UserInfo持久化标识所对应的表记录；然后自动生成一个持久化状态的UserInfo实体，与脱管状态的UserInfo实体做比较是否有所改变；一旦发生了改变，才会发送update语句执行更新。而按执行顺序，若两句session.merge()方法针对同一个脱管状态的UserInfo实体，那其结果只会执行最后一个session.merge()方法所发出的update语句。即使执行了session.merge()方法，UserInfo实体依然是脱管状态，

错误日志

严重: Servlet.service() for servlet [my-one] in context with path [/myone-web] threw exception [Request processing failed; nested exception is org.springframework.dao.DuplicateKeyException: A different object with the same identifier value was already associated with the session : [com.dabai.pojo.Privilege#2]; nested exception is org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [com.dabai.pojo.Privilege#2]] with root cause
org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [com.dabai.pojo.Privilege#2]
    at org.hibernate.engine.internal.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:648)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:284)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:227)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:92)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
    at org.hibernate.internal.SessionImpl.fireSaveOrUpdate(SessionImpl.java:648)
    at org.hibernate.internal.SessionImpl.saveOrUpdate(SessionImpl.java:640)
    at org.hibernate.engine.spi.CascadingActions$5.cascade(CascadingActions.java:218)
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:398)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:323)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:162)
    at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:431)
    at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:363)
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:326)
    at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:162)
    at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:111)
    at org.hibernate.event.internal.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:150)
    at org.hibernate.event.internal.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:141)
    at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:74)
    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:38)
    at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1282)
    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:465)
    at org.hibernate.internal.SessionImpl.flushBeforeTransactionCompletion(SessionImpl.java:2963)
    at org.hibernate.internal.SessionImpl.beforeTransactionCompletion(SessionImpl.java:2339)
    at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.beforeTransactionCompletion(JdbcCoordinatorImpl.java:485)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.beforeCompletionCallback(JdbcResourceLocalTransactionCoordinatorImpl.java:147)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl.access$100(JdbcResourceLocalTransactionCoordinatorImpl.java:38)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:231)
    at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:65)
    at org.springframework.orm.hibernate5.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:581)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:761)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:730)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:485)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:291)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:208)
    at com.sun.proxy.$Proxy46.editRole(Unknown Source)