自己遇到的hibernate错误

1 . a different object with the same identifier value was already associated with the session: [VoBean.Employee#2]
  原因：session中已经存在相同的对象，一般发生在级联修改该对象的set集合中对象已经存在相同的对象　
解决：对象的set集合设置为一个空的set集合！
  
2.object references an unsaved transient instance - save the transient instance before flushing: VoBean.Department;
 nested exception is org.hibernate.TransientObjectException: object references an unsaved transient instance - save the
 transient instance before flushing: VoBean.Department 
原因：  一个对象引用了一个没有保存对象(一般该对象为null)

解决 : 确保引用对象不为空