Hibernate 保存惰性子对象会导致：TransientObject异常：对象引用未保存的临时实例-在刷新之前保存临时实例

我正在hibernate中尝试惰性加载实体，但无法克服上述错误。我基本上在玩两个实体：用户和角色：

public class User implements Serializeable {
    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "T_USER_ROLE", joinColumns = @JoinColumn(name = "USER_ID"), inverseJoinColumns = @JoinColumn(name = "ROLE_ID"))
    private Set<Role> roles = new HashSet<Role>();
}

public class Role implements Serializeable { }

然后，在设置角色和更新之前，我尝试先持久化用户实体，但也失败了：

userService.create(user);
User user = userService.findById(user.getId());
Set<Role> roles = new HashSet<Role>();
roles.add(roleService.findByName(RolesEnum.MEMBER.toString()));
user.setRoles(roles);
userService.update(user, true);

---

通过将实体管理器绑定到对话范围并使用seam焊料，可以解决此问题

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER, ElementType.TYPE })
public @interface TempJpa { }

@ExtensionManaged
@ConversationScoped
@Produces
@PersistenceUnit(unitName="tempDataSource")
@TempJpa
private EntityManagerFactory emf;

@Inject
@TempJpa
protected EntityManager em;

但下一个问题是为什么

java.lang.IllegalStateException: org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.test.Role org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1374)

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER, ElementType.TYPE })
public @interface TempJpa { }

@ExtensionManaged
@ConversationScoped
@Produces
@PersistenceUnit(unitName="tempDataSource")
@TempJpa
private EntityManagerFactory emf;

@Inject
@TempJpa
protected EntityManager em;