Hibernate在查询中重新加载实体时遇到问题,即使它们是作为主查询的一部分来获取的。

实体如下(简化)

class Data {
    @Id
    String guid;

    @ManyToOne(fetch = FetchType.LAZY)
    @NotFound(action = NotFoundAction.IGNORE)
    DataContents contents;
}

class DataClosure {
    @Id
    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "ancestor_id", nullable = false)
    private Data ancestor;

    @Id
    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "descendant_id", nullable = false)
    private Data descendant;

    private int length;
}


这是建模父/子关系的关闭表。

我建立了一些标准如下

    final Criteria criteria = getSession()
            .createCriteria(DataClosure.class, "dc");
    criteria.createAlias("dc", "a");
    criteria.createAlias("dc.descendant", "d");
    criteria.setFetchMode("a", FetchMode.JOIN);
    criteria.setFetchMode("d", FetchMode.JOIN);
    criteria.add(Restrictions.eq("d.metadataGuid",guidParameter));
    criteria.add(Restrictions.ne("a.metadataGuid",guidParameter));


这导致以下SQL查询

select
    this_.descendant_id as descenda2_21_2_,
    this_.ancestor_id as ancestor3_21_2_,
    this_.length as length1_21_2_,
    d2_.guid as metadata1_20_0_,
    d2_.name as name5_20_0_,
    a1_.guid as metadata1_20_1_,
    a1_.name as name6_20_1_
from
    data_closure this_
inner join
    data d2_
        on this_.descendant_id=d2_.metadata_guid
inner join
    data a1_
        on this_.ancestor_id=a1_.metadata_guid
where
    d2_.guid=?
    and a1_.guid<>?


看起来好像正确地实现了连接提取。但是当我执行

    List list = criteria.list();


我在结果集中每行的SQL日志中看到这些条目之一

Result set row: 0
DEBUG Loader  - Loading entity: [Data#testGuid19]
DEBUG SQL  -
select
    data0_.guid as guid1_20_0_,
    data0_.title as title5_20_0_,
from
    data data0_
where
    data0_.guid=?
Hibernate:
   (omitted)
DEBUG Loader  - Result set row: 0
DEBUG Loader  - Result row: EntityKey[Data#testGuid19]
DEBUG TwoPhaseLoad  - Resolving associations for [Data#testGuid19]
DEBUG Loader  - Loading entity: [DataContents#7F1134F890A446BBB47F3EB64C1CF668]
DEBUG SQL  -
select
    dataContents0_.guid as guid_12_0_,
    dataContents0_.isoCreationDate as isoCreat2_12_0_,
from
    dataContents dataContents0_
where
    dataContents0_.guid=?
Hibernate:
    (omitted)


看起来即使DataContents被标记为延迟加载,它仍在急切地加载。

因此,我要么希望查询中的某种方式来获取联接DataClosure和Data并懒惰地获取DataContents,要么如果不可能,则获取联接DataContents。

编辑:

像这样建模闭合表

class DataClosure {
    @Id
    @Column(name = "ancestor_id", nullable = false, length =36 )
    private String ancestorId;

    @Id
    @Column(name = "descendant_id", nullable = false, length =36 )
    private String descendantId;

    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "ancestor_id", nullable = false)
    private Data ancestor;

    @ManyToOne(fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    @JoinColumn(name = "descendant_id", nullable = false)
    private Data descendant;

    private int length;
}


解决了问题。换句话说,即使生成的查询没有问题,对来自其他表的实体使用@Id注释似乎也可能导致此问题。

最佳答案

我认为您的问题可能是这个

@NotFound(action = NotFoundAction.IGNORE)


有大量的google结果,其中使用会导致延迟加载变得迫切。我认为这是Hibernate中的错误。

将其添加到注释列表中可以解决此问题

@LazyToOne(value=LazyToOneOption.NO_PROXY)


由于这会通知Hibernate您以后将不再尝试使用该属性,因此不需要代理。

09-05 15:29
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