jpa hibernate（1） 多对多，用户新增，只增加中间表对应角色关系，不增加角色role

User实体:
@ManyToMany(cascade = {CascadeType.MERGE})
@JsonIgnore
@JoinTable(name = "CMSUserRole",
joinColumns = { @JoinColumn(name = "userid", referencedColumnName = "userid") },
inverseJoinColumns = { @JoinColumn(name = "roleid", referencedColumnName = "roleid") })
private Collection<Role> roles;

Role实体:
@ManyToMany(mappedBy = "roles")
@Basic(fetch = FetchType.LAZY)
private Collection<User> users;

controller中：
@RequestMapping(value = "add",method= RequestMethod.POST)
@ResponseBody
public boolean register(User user){
Role role=new Role();
role.setId((long) 2);
Set<Role> roles=new HashSet<Role>();
roles.add(role);
user.setRoles(roles) ;
return userService.insert(user);
}