休眠重新加载提取联接中的实体

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，如下所示

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));

这将导致以下 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<>?

看起来它正在正确实现联接提取。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)

看起来即使数据内容被标记为延迟加载，它也在急切地加载。

因此，我要么想要在我的查询中以某种方式获取连接 DataClosure 和数据并懒惰地获取 DataContent，要么如果不可能，则获取连接 DataContent。

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;
}

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

我认为你在这里的问题可能是这个

@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中应该可以解决问题

@LazyToOne(value=LazyToOneOption.NO_PROXY)

由于这会通知 Hibernate您以后不会尝试使用该属性，因此不需要代理。