postgresql 取相同对象到N层,取不同对象到N层

eoxn13cs  于 2023-02-04  发布在  PostgreSQL
关注(0)|答案(1)|浏览(133)

所以我想获取整个树结构的XmlObject,对象有父子OneToMany关系,childObjects到自己和OneToMany关系到xmlPeriods,xmlPeriods只在最后一级。
树是这样的。

XmlObject

  |_XmlObject

     |_XmlObject

       |_XmlObject

         |_XmlPeriod

以下是我的实体的关系。

@Entity
@Table(name = "xml_object")
public class XmlObject implements Serializable {

    @Fetch(value = FetchMode.SELECT)
    @BatchSize(size = 50)
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
    @JoinTable(
            name = "xml_object_tree",
            joinColumns = {@JoinColumn(name = "parent_id", referencedColumnName = "id")},
            inverseJoinColumns = {@JoinColumn(name = "child_id", referencedColumnName = "id")}
    )
    @ToString.Exclude
    private List<XmlObject> childObjects;

    @Fetch(value = FetchMode.SUBSELECT) // FetchMode.JOIN loads eagerly always
    @OneToMany(cascade = {CascadeType.ALL}, fetch = FetchType.LAZY, orphanRemoval = false)
    @JoinColumn(name = "xml_object_id", nullable = false)
    @ToString.Exclude
    private List<XmlPeriod> xmlPeriods;

我从这个查询开始。

@Query(value = "select xo.id from XmlObject xo " +
            " where xo.objectType = :type and bw_and(xo.status, :status) = 0")
    Optional<List<Long>> findAllObjectsIdsOfTypeAndNotInStatusesAndNotDeletedN(
            ObjectTypeEnum type, Integer status, Pageable pageable);
  • bw_and* -通过自定义Postgres方言按位应用 and

我不想设置fetch = FetchType.EAGER,我不想在下面的“设置为抑制错误”下隐藏问题

cannot simultaneously fetch multiple bags

我不能使用来自Vlad Mihalcea的两个查询solution,因为对象引用了自己,xmlPeriod位于最后一级。
从那篇文章中我不明白如何请求查尔兹的完整树,我可以使用下面的代码请求第一级,但是如何请求N?

private Set<XmlObject> getXOToProcessVM() {

        List<XmlObject> xmlObjects = entityManager.createQuery(
                        " select distinct p " +
                                " from XmlObject p " +
                                " left join fetch p.childObjects " +
                                " where p.id between :minId and :maxId", XmlObject.class)
                .setParameter("minId", 1L)
                .setParameter("maxId", 50L)
                .setHint(QueryHints.PASS_DISTINCT_THROUGH, false)
                .getResultList();

        xmlObjects = entityManager.createQuery(
                        " select distinct p " +
                                " from XmlObject p " +
                                " left join fetch p.childObjects " +
                                " where p in :xmlObjects", XmlObject.class)
                .setParameter("xmlObjects", xmlObjects)
                .setHint(QueryHints.PASS_DISTINCT_THROUGH, false)
                .getResultList();

        return Set.copyOf(xmlObjects);
        
    }

除了其他尝试,我还尝试了这个存储库中的本地查询,从Postgres的Angular 来看,这似乎是我真正需要的

@Query(value = "select DISTINCT * from xml_object message " +
            " left join xml_object_tree tree1 on message.id = tree1.parent_id " +
            " left join xml_object sender on sender.id = tree1.child_id " +
            " left join xml_object_tree tree2 on sender.id = tree2.parent_id " +
            " left join xml_object area on area.id = tree2.child_id " +
            " left join xml_object_tree tree3 on area.id = tree3.parent_id " +
            " left join xml_object measuringPoint on measuringPoint.id = tree3.child_id " +
            " left join xml_object_tree tree4 on measuringPoint.id = tree4.parent_id " +
            " left join xml_object measuringChannel on measuringChannel.id = tree4.child_id " +
            " left join xml_period period on period.xml_object_id = measuringChannel.id " +
            " where message.id IN :ids", nativeQuery = true)
    Set<XmlObject> findAllObjectsByIdsFetchChildsAndPeriods(Iterable<Long> ids);

但是它为连接的每个对象原因返回几行,这是不可接受的。
我已经尝试了这个查询从Hibernate的Angular 来看,但它只提取第一级的查尔兹,但我需要所有的树加上XmlPeriods从最后一级。不能使用几个JOIN FETCH原因笛卡尔积(集)和JPA限制(列表)

@Query(value = "select xo from XmlObject xo " +
            " join fetch xo.childObjects senders " +
            " where xo.id IN :ids")
    List<XmlObject> findAllObjectsByIdsFetchingChilds(Iterable<Long> ids);

68bkxrlz

68bkxrlz1#

您将需要一个递归CTE来对此建模,并且由于Hibernate不支持递归获取连接,因此您还必须自己构建对象图。
我们的想法是这样编写一个HQL查询:

with nodes as (
    select :rootId as id, null as parentId
    from (values (1)) t(x)

    union all

    select c.id as id, xo.id as parentId
    from XmlObject xo 
    join nodes n on xo.id = n.id 
    join xo.childObjects c
)
select o, n.parentId
from nodes n
join XmlObject o on o.id = n.id
left join fetch o.xmlPeriods

您将需要Hibernate 6.2或Blaze-Persistence。
结果是所有节点的列表,然后您只需正确地连接它们

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