Question

我遇到了Hibernate在查询中重新加载实体的问题，即使它们是作为主查询的一部分被提取的。

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/子关系的闭包表。

我已经设置了以下标准

    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<>?

看起来它正确实现了连接提取。但是当我执行

时

    List list = criteria.list();

我在结果集

中每行的SQL日志中看到其中一个条目

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)

即使DataContents被标记为延迟加载，看起来也是如此，但它正在急切地加载。

所以我要么在我的查询中想要一些方法来获取连接DataClosure和Data并且懒惰地获取DataContents，或者如果不可能那么获取加入DataContents。

编辑：

像这样建模闭包表

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;
}

修复了问题。换句话说，对其他表中的实体进行@Id注释似乎会导致问题，即使生成的查询没有任何问题。

Answer 1

我认为你的问题可能就是这个

@NotFound(action = NotFoundAction.IGNORE)

有很多谷歌搜索结果会导致延迟加载变得急切。我认为这是Hibernate中的一个错误。

将其添加到注释列表中应解决问题

@LazyToOne(value=LazyToOneOption.NO_PROXY)

因为它告诉Hibernate你以后不会尝试使用该属性所以不需要代理。

Hibernate在获取连接中重新加载实体

1 个答案: