java - Hibernate 在获取连接中重新加载实体

Question

我在 Hibernate 重新加载查询中的实体时遇到问题，即使它们是作为主查询的一部分获取的。

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;
}

这是对父/子关系的闭包表进行建模。

我设置了一些标准如下

    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));

这会产生以下 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<>?

看起来它正确地实现了连接获取。但是当我执行时

    List list = criteria.list();

我在结果集中的每行 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)

看起来即使 DataContents 被标记为延迟加载，它也会被急切地加载。

因此，我要么希望在查询中以某种方式获取联接 DataClosure 和数据并延迟获取 DataContents，要么在不可能的情况下获取联接 DataContents。

编辑:

像这样对闭包表进行建模

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任何问题，对其他表中的实体使用 @Id 注释似乎也会导致问题。

Answer 1

我认为你的问题可能是这样的

@NotFound(action = NotFoundAction.IGNORE)

有很多谷歌结果，使用它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应该可以解决问题

@LazyToOne(value=LazyToOneOption.NO_PROXY)

因为这会通知 Hibernate 您稍后不会尝试使用该属性，因此不需要代理。