java – Spring数据jpa分离实体

此关系在User类中定义如下：

@ManyToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
@JoinTable(name="user_role",joinColumns = {@JoinColumn(name="user_id")},inverseJoinColumns = {@JoinColumn(name="role_id")})
private Set<UserRole> roles;

我用以下方法创建角色

@Transactional
private void generateSeedRoles() {
    UserRole adminRole = new UserRole(RoleEnum.ADMIN.toString());
    userRoleRepository.save(adminRole);

    UserRole userRole = new UserRole(RoleEnum.USER.toString());
    userRoleRepository.save(userRole);
}

之后为用户分配角色失败：

@Transactional
private void generateSeedUsers() {
    UserRole adminRole = userRoleRepository.findUserRoleByRoleName("ADMIN");

    User user = User.createUser("user1","user1@user.com","pass");
    user.setRoles(new HashSet<UserRole>(Arrays.asList(adminRole)));

    userRepository.save(user);
}

抛出以下异常(为便于阅读而格式化)：

org.springframework.dao.InvalidDataAccessApiUsageException: 
detached entity passed to persist: co.feeb.models.UserRole; 
nested exception is org.hibernate.PersistentObjectException: 
detached entity passed to persist: co.feeb.models.UserRole

但是,如果在创建关系之前保存用户,则它可以正常工作：

@Transactional
private void generateSeedUsers() {
    UserRole adminRole = userRoleRepository.findUserRoleByRoleName("ADMIN");

    User user = User.createUser("user1","pass");
    //Save user
    userRepository.save(user);

    //Build relationship and update user
    user.setRoles(new HashSet<UserRole>(Arrays.asList(adminRole)));
    userRepository.save(user);
}

必须保存/更新用户两次对我来说似乎有些不合理.有没有办法将收到的角色分配给新用户而不先保存用户？