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。