hibernate - JPA 2.1 通过提示查找，如果@NamedEntityGraph 中存在多个@NamedSubgraph，则返回冗余结果

Question

我在我的项目中结合使用 **JPA 2.1** 和 **Hibernate 5.0.2.final**。

问题是，当我加载类型为 {@EventTO} 的实例时，如果该实例一次没有与会者和 assignedResources 或这些集合之一，它将正确加载；但是，如果它同时拥有这两个集合，则实体图的提取结果将携带冗余数据。例如，如果有 3 个与会者和 2 个 assignedResources，作为线索，它将返回 4 个与会者和 3 个 assignedResources。我对这样的行为感到困惑。我不知道为什么？？？。可能与 hibernate 查询有关，但我不确定。

现在，如果有人能帮我找到解决这个问题的天才解决方案，我将不胜感激。

提到的实体以及调用 JPA 实体管理器的 find 方法的代码片段如下:

EventTO 实体:

@Entity
@Table(name = "CALT_EVENT")
@SequenceGenerator(name = "seq", sequenceName = "seq_cal_event", allocationSize = 1)
@NamedEntityGraph(name = "loadGraph",
            attributeNodes = {
                    @NamedAttributeNode(value = "attendees", subgraph = "attendees"),
                    @NamedAttributeNode(value = "assignedResources", subgraph = "assignedResources")
            },

            subgraphs = {
                    @NamedSubgraph(name = "attendees", attributeNodes = {@NamedAttributeNode("departmentAttendee"), @NamedAttributeNode(value = "personAttendee")}),
                    @NamedSubgraph(name = "assignedResources", attributeNodes = @NamedAttributeNode("resourceTO"))
            }
    )
})
public class EventTO {
    private List<EventAttendeeTO> attendees = new ArrayList<EventAttendeeTO>();
    private List<EventAssignedResourceTO> assignedResources = new  ArrayList<EventAssignedResourceTO>();

    /**
     * @return the attendeesTOList
     */
     @OneToMany(mappedBy = "eventTO", cascade = CascadeType.ALL, orphanRemoval = true)
     public List<EventAttendeeTO> getAttendees() {
         return attendees;
     }

     /**
      * @param attendees the attendeesTOList to set
      */
     public void setAttendees(List<EventAttendeeTO> attendees) {
        if (attendees != null) {
            this.attendees = attendees;
        }
    }

    /**
     * @return the assignedResourceTOList
     */
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "eventTO", orphanRemoval = true)
    public List<EventAssignedResourceTO> getAssignedResources() {
        return assignedResources;
    }

    /**
     * @param assignedResources the assignedResourceTOList to set
     */
    public void setAssignedResources(List<EventAssignedResourceTO> assignedResources) {
        if (assignedResources != null) {
            this.assignedResources = assignedResources;
        }
    }
}

EventAttendeeTO 实体:

@Entity
@Table(name = "CALT_EVENT_ATTENDEES")
@SequenceGenerator(name = "seq", sequenceName = "seq_cal_event_attendees", allocationSize = 1)
public class EventAttendeeTO extends RecordableExtEntityTO {
    private EventTO eventTO;
    private PersonTO personAttendee;
    private DepartmentTO departmentAttendee;

    /**
     * @return the eventTO
     */
    @JSON(serialize = false)
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "EAT_EVN_ID", nullable = false)
    public EventTO getEventTO() {
        return eventTO;
    }

    /**
     * @param eventTO
     *            the eventTO to set
     */
    public void setEventTO(EventTO eventTO) {
        this.eventTO = eventTO;
    }

    /**
     * @return the attendee
     */
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "EAT_PER_ID")
    public PersonTO getPersonAttendee() {
        return personAttendee;
    }

    /**
     * @param personAttendee
     *            the personAttendee to set
     */
    public void setPersonAttendee(PersonTO personAttendee) {
        this.personAttendee = personAttendee;
        if (personAttendee != null) {
            this.perId = personAttendee.getId();
        }
   }        

}

EventAssignedResourceTO 实体:

@Entity
@Table(name = "CALT_EVENT_ASSIGNED_RESOURCE")
@SequenceGenerator(name = "seq", sequenceName = "seq_cal_event_assigned_res", allocationSize = 1)
public class EventAssignedResourceTO extends ExtEntityTO {

    private EventTO eventTO;
    private EventResourceTO resourceTO;

   /**
    * @return the eventTO
    */
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "EAR_EVN_ID", nullable = false)
    public EventTO getEventTO() {
        return eventTO;
    }   

    /**
     * @param eventTO
     *            the eventTO to set
     */
    public void setEventTO(EventTO eventTO) {
        this.eventTO = eventTO;
    }

   /**
    * @return the resourceTO
    */
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "EAR_ERS_ID")
    public EventResourceTO getResourceTO() {
        return resourceTO;
    }

    /**
     * @param resourceTO
     *            the resourceTO to set
     */
    public void setResourceTO(EventResourceTO resourceTO) {
        this.resourceTO = resourceTO;
    }
}

通过hint方式调用entity manager的find方法的代码片段:

    try {
        EntityGraph graph = this.em.getEntityGraph("loadGraph");
        Map hints = new HashMap();
        hints.put("javax.persistence.fetchgraph", graph);
        return em.find(EventTO.class, id, hints);             
    } catch (Exception e) {
        new DAOException(e);
    }

Answer 1

在修改我的代码并仔细思考这个问题之后，我想到了以下原因:
此问题可能与 hibernate 在同时加载多个集合方面的限制有关。由于我的 ORM 处于 hibernate 状态，因此在获取我的 TO 时可能会出现这样的问题。

更多详细信息:Hibernate 在一次查询中获取多个包时抛出以下异常:

org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags

也许使用 NamedGraph 会导致 hibernate 创建基于错误的外部左连接的查询，这会导致获取冗余或换句话说无效数据。