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。

我制定了以下一些标准

    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<>?

看起来它正确地实现了连接获取。但是当我执行

    List list = criteria.list();

我在结果集中的每行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被标记为懒加载，它也在急切地加载。

因此，我要么希望在我的查询中以某种方式获取加入数据闭包和数据并懒惰地获取数据内容，要么在不可能的情况下获取加入数据内容。

编辑：

像这样模拟关闭表

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，尽管生成的查询没有任何问题。

Answer 1

我想你的问题可能是这个

@NotFound(action = NotFoundAction.IGNORE)

有很多google结果，使用它会导致懒惰加载变得急切。我认为这是Hibernate中的一个错误。

将此添加到注释列表中应该可以解决此问题

@LazyToOne(value=LazyToOneOption.NO_PROXY)

因为这会通知Hibernate您以后不会尝试使用该属性，所以不需要代理。