如何在 join fetch QueryDSL JPAQuery 中选择

Question

我有一个带有QueryDSL JPAQuery的应用程序。在这里：

JPAQuery<MyWrapper> searchQuery
        = queryFactory.select(Projections.constructor(MyWrapper.class,
        deviceGroup.id,
        deviceGroup.name,
        deviceGroup.orientation,
        deviceGroup.location,
        deviceGroup.customer,
        workgroup.account,
        Expressions.as(queryFactory.select(device.count())
            .from(device)
            .where(device.group.id.eq(deviceGroup.id)), "displaysQty"),
        Expressions.as(queryFactory.select(device.count())
            .from(device)
            .where(device.group.id.eq(deviceGroup.id),
                device.status.eq(DeviceStatus.HEALTHY)), "healthyQty"),
        Expressions.as(queryFactory.select(device.count())
            .from(device)
            .where(device.group.id.eq(deviceGroup.id),
                device.status.eq(DeviceStatus.NO_SYNC)), "noSyncQty"),
        Expressions.as(queryFactory.select(device.count())
            .from(device)
            .where(device.group.id.eq(deviceGroup.id),
                device.status.eq(DeviceStatus.NEED_SERVICE)), "needServiceQty"),
        Expressions.as(queryFactory.select(device.count())
            .from(device)
            .where(device.group.id.eq(deviceGroup.id),
                device.status.eq(DeviceStatus.OUT_OF_SERVICE)), "outOfServiceQty")))
        .from(deviceGroup)
        .leftJoin(deviceGroup.customer, workgroup).fetchJoin()
        .leftJoin(workgroup.account, account).fetchJoin()
        .where(predicate)
        .orderBy(sortingParams.toArray(new OrderSpecifier[0]));

MyWrapper 看起来像：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class MyWrapper{
  private Long id;
  private String name;
  private DsmsOrientationType orientation;
  private String location;
  private WorkgroupEntityJpa customer;
  private AccountEntityJpa account;
  private long displaysQty;
  private long healthyQty;
  private long noSyncQty;
  private long needServiceQty;
  private long outOfServiceQty;
}

我已经指定了异常查询连接获取，但获取关联的所有者不在选择列表中。

我已经尝试了deviceGroup.customer.account而不是workgroup.account，结果是一样的。

UPD下面是 JPAQuery.toString（）：

select deviceGroupEntityJpa.id, 
        deviceGroupEntityJpa.name, 
        deviceGroupEntityJpa.orientation, 
        deviceGroupEntityJpa.location, 
        deviceGroupEntityJpa.customer, 
        workgroupEntityJpa.account, 
        (select count(deviceEntityJpa)
            from DeviceEntityJpa deviceEntityJpa
            where deviceEntityJpa.group.id = deviceGroupEntityJpa.id) as displaysQty, 
        (select count(deviceEntityJpa)
            from DeviceEntityJpa deviceEntityJpa
            where deviceEntityJpa.group.id = deviceGroupEntityJpa.id and deviceEntityJpa.status = ?1) as healthyQty, 
        (select count(deviceEntityJpa)
            from DeviceEntityJpa deviceEntityJpa
            where deviceEntityJpa.group.id = deviceGroupEntityJpa.id and deviceEntityJpa.status = ?2) as noSyncQty, 
        (select count(deviceEntityJpa)
            from DeviceEntityJpa deviceEntityJpa
            where deviceEntityJpa.group.id = deviceGroupEntityJpa.id and deviceEntityJpa.status = ?3) as needServiceQty, 
        (select count(deviceEntityJpa)
            from DeviceEntityJpa deviceEntityJpa
            where deviceEntityJpa.group.id = deviceGroupEntityJpa.id and deviceEntityJpa.status = ?4) as outOfServiceQty
from DeviceGroupEntityJpa deviceGroupEntityJpa
  left join fetch deviceGroupEntityJpa.customer as workgroupEntityJpa
  left join fetch workgroupEntityJpa.account as accountEntityJpa

Answer 1

根据错误消息，此处不需要联接提取，因为这是一个性能提示，会强制预先加载集合。

因此，请使用常规联接而不是联接提取。

Answer 2

由于您有 DTO 投影，因此 FETCH 指令在这里没有意义。fetch 指令告诉 Hibernate 将关联包含在 SELECT 子句中，但您不希望这样做，因为 DTO 投影不需要 FETCH 指令。

像这样：

SELECT new EmployeeDTO(e.obj1,e.obj2,e.obj3,e.startDate,e.endDate) 
FROM Employee e 
left outer join fetch e.obj1  
left outer join fetch e.obj2 
left outer join fetch e.obj3

由于上述原因不起作用。

溶液

只需删除 fetch 关键字即可。