hibernate注解多对多级联保存怎么解

@ManyToMany(mappedBy="sysUsers",cascade={CascadeType.PERSIST,CascadeType.MERGE}) 
private Set<SysDept> sysDept = new HashSet<SysDept>(0);   //部门

 @ManyToMany(
         cascade={CascadeType.PERSIST,CascadeType.MERGE},fetch=FetchType.EAGER)
 @JoinTable(name="sys_user_depart" ,joinColumns={@JoinColumn(name="departId")},inverseJoinColumns={@JoinColumn(name="userId")})
 @OrderBy("id ASC")
private Set<SysUsers> sysUsers = new HashSet<SysUsers>(0);

有一张中间表
为什么不能级联保存

http://blog.csdn.net/a5489888/article/details/6858026