Java 继承JPA和Hibernate问题
我在加载一些对象时遇到了一个奇怪的问题。我使用的是JPA1、hibernate core版本3.3.0.SP1和hibernate entitymanager版本3.4.0.GA 假设我有这些JPA实体:Java 继承JPA和Hibernate问题,java,hibernate,inheritance,jpa,Java,Hibernate,Inheritance,Jpa,我在加载一些对象时遇到了一个奇怪的问题。我使用的是JPA1、hibernate core版本3.3.0.SP1和hibernate entitymanager版本3.4.0.GA 假设我有这些JPA实体: @Entity @Table(name = "SLC_ELE") @Inheritance(strategy = InheritanceType.JOINED) @DiscriminatorColumn(discriminatorType = DiscriminatorType.INTEGER
@Entity
@Table(name = "SLC_ELE")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(discriminatorType = DiscriminatorType.INTEGER, name = ElementoPrograma.C_ID_CTG_ELE)
public class Element {
...
}
@Entity
@Table(name = "SLC_ELE_ONE")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorValue(Categories.ID_CTG_ONE)
public class ElementTypeOne extends Element {
...
}
@Entity
@Table(name = "SLC_ELE_TWO")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorValue(Categories.ID_CTG_TWO)
public class ElementTypeTwo extends Element {
...
}
@Entity
@Table(name = ThreeElementExample.TABLENAME)
@AssociationOverrides({
@AssociationOverride(name = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_ONE,
joinColumns =
@JoinColumn(name = Element.C_ID_ELE)),
@AssociationOverride(name = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_TWO,
joinColumns =
@JoinColumn(name = OneEntity.C_ID_TWO)),
@AssociationOverride(name = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_THREE,
joinColumns =
@JoinColumn(name = AnotherEntity.C_ID_THREE))})
public class ThreeElementExample extends JpaMany3ManyEntity<Element, OneEntity, AnotherEntity> {
...
}
@实体
@表(name=“SLC_ELE”)
@继承(策略=InheritanceType.JOINED)
@DiscriminatorColumn(discriminatorType=discriminatorType.INTEGER,name=ElementoPrograma.C_ID_CTG_ELE)
公共类元素{
...
}
@实体
@表(name=“SLC\u ELE\u ONE”)
@继承(策略=InheritanceType.JOINED)
@鉴别器值(Categories.ID\u CTG\u ONE)
公共类ElementTypeOne扩展元素{
...
}
@实体
@表(name=“SLC\u ELE\u TWO”)
@继承(策略=InheritanceType.JOINED)
@鉴别器值(Categories.ID\u CTG\u TWO)
公共类ElementTypeTwo扩展元素{
...
}
@实体
@表(名称=ThreeElementExample.TABLENAME)
@联想超越({
@AssociationOverride(name=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u ONE,
连接柱=
@JoinColumn(name=Element.C_ID_ELE)),
@AssociationOverride(name=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u TWO,
连接柱=
@JoinColumn(name=OneEntity.C_ID_TWO)),
@AssociationOverride(name=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u三、,
连接柱=
@JoinColumn(name=AnotherEntity.C_ID_THREE))})
公共类ThreeElementExample扩展了JpaMany3ManyEntity{
...
}
问题是,当我加载这些实体的集合时,我希望总是获得子类(意味着ElementTypeOne,ElementTypeTwo而不是元素)。问题是多对多关系总是得到元素(父亲而不是孩子)
假设我有一个包含元素集合的实体A:
@Fetch(FetchMode.JOIN)
@OneToMany(cascade = CascadeType.ALL, mappedBy = "idEle")
private Collection<Element> elementCollection;
@Fetch(FetchMode.JOIN)
@OneToMany(cascade=CascadeType.ALL,mappedBy=“idEle”)
私人收藏元素收藏;
如果我得到了集合,一切都很好(我得到了预期的子类)
当我有另一个实体B和JpaMany3ManyEntity的集合时,问题就来了(注意,涉及的是同一个实体元素)
@OneToMany(cascade=CascadeType.ALL,mappedBy=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u ONE,fetch=FetchType.LAZY)
私人收藏三要素示例收藏;
如果我在尝试从类A获取elementCollection之前循环类B中的threeElementExampleCollection,那么当我从elementCollection加载对象时
我只获得超类(元素)对象,而不是子对象
我猜想,出于任何原因,多对多关系总是获取元素对象(父对象)并将它们保存在hibernate缓存中,但我需要避免这种行为
有什么想法或想法吗?任何形式的帮助都将不胜感激
提前谢谢
编辑:多对多类:
@SuppressWarnings("serial")
@MappedSuperclass
@AssociationOverrides({
@AssociationOverride(name = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_ONE,
joinColumns =
@JoinColumn(name = "changeMeWhenExtends")),
@AssociationOverride(name = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_TWO,
joinColumns =
@JoinColumn(name = "changeMeWhenExtends")),
@AssociationOverride(name = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_THREE,
joinColumns =
@JoinColumn(name = "changeMeWhenExtends"))})
public abstract class JpaMany3ManyEntity<A extends JpaBaseEntity, B extends JpaBaseEntity, C extends JpaBaseEntity> extends JpaBaseEntity {
public static final String ID_ATTNAME = "id";
public static final String ASOCIATION_OVERRIDE_ONE = JpaMany3ManyEntity.ID_ATTNAME + "." + JpaMany3ManyId.ID_ONE_ATTNAME;
public static final String ASOCIATION_OVERRIDE_TWO = JpaMany3ManyEntity.ID_ATTNAME + "." + JpaMany3ManyId.ID_TWO_ATTNAME;
public static final String ASOCIATION_OVERRIDE_THREE = JpaMany3ManyEntity.ID_ATTNAME + "." + JpaMany3ManyId.ID_THREE_ATTNAME;
...
}
@SuppressWarnings(“串行”)
@映射超类
@联想超越({
@AssociationOverride(name=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u ONE,
连接柱=
@JoinColumn(name=“changeMwhenextends”),
@AssociationOverride(name=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u TWO,
连接柱=
@JoinColumn(name=“changeMwhenextends”),
@AssociationOverride(name=jpamany3manyintentity.ASOCIATION\u OVERRIDE\u三、,
连接柱=
@JoinColumn(name=“changemewehenextends”))})
公共抽象类JpaMany3ManyEntity扩展了JpaBaseEntity{
公共静态最终字符串ID\u ATTNAME=“ID”;
public static final String ASOCIATION\u OVERRIDE\u ONE=JpaMany3ManyEntity.ID\u ATTNAME+““+JpaMany3ManyId.ID\u ONE\u ATTNAME;
public static final String ASOCIATION\u OVERRIDE\u TWO=JpaMany3ManyEntity.ID\u ATTNAME+““+JpaMany3ManyId.ID\u TWO\u ATTNAME;
public static final String ASOCIATION\u OVERRIDE\u THREE=JpaMany3ManyEntity.ID\u ATTNAME+““+JpaMany3ManyId.ID\u THREE\u ATTNAME;
...
}
这里有一个对我有效的工作区:解除实体的代理权
即使有实体的父代理(jpa.heritation.issue.Element\u$$\ uJavassist\u1),如果将其解除代理,也将获得真实的实体(子实体)
假设您希望循环实体A中的(子)元素集合,并对它们进行处理
比如:
public void loopDeproxyElements(List<Element> yourElementsCollection){
for(Element p : yourElementsCollection){
if(p instanceof HibernateProxy){
Element child = (Element) ((HibernateProxy) p).getHibernateLazyInitializer()
.getImplementation();
if (child instanceof ElementTypeOne){
//You can cast your object or do whatever you want, knowing for sure that's a child element)
ElementTypeOne myRealElement = (ElementTypeOne) child;
...
} else {
//It should be ElementTypeTwo (if u never create parent entities)
...
}
}
}
)
public void loopDeproxyElements(列出您的元素集合){
for(元素p:yourElementsCollection){
if(HibernateProxy的p实例){
元素子元素=(元素)((HibernateProxy)p).getHibernateLazyInitializer()
.getImplementation();
if(ElementTypeOne的子实例){
//你可以投射你的对象或做任何你想做的事情,确信那是一个子元素)
ElementTypeOne myRealElement=(ElementTypeOne)子级;
...
}否则{
//它应该是ElementTypeTwo(如果您从未创建父实体)
...
}
}
}
)
它将始终像我所期望的那样获取子元素。尝试使用
hibernate。默认的\u batch\u fetch\u size
属性。默认情况下,它设置为1。这将只加载集合中的第一个实体。将它增加到集合的~size可能会有所帮助。是否介意添加jpamany3manyintentity的定义
完整性?没问题,但我很确定问题不在这里。无论如何,这个问题已经编辑好了。你能添加示例代码说明你如何实际使用它吗?这实际上是一个基于问题中定义的类的示例,你从一个惰性集合中获取值,但对值进行反代理ining始终是实体的真实类型。这意味着p是集合中的一个元素。“p”在哪里来自?我已编辑了答案。我希望它能帮助您了解deproxy的实际工作原理。您的答案容易受到ClassCastException
的攻击。在强制执行之前,请检查p HibernateProxy的instanceof
。有时在缓存中找到实体时,它可能已经被加载。
public void loopDeproxyElements(List<Element> yourElementsCollection){
for(Element p : yourElementsCollection){
if(p instanceof HibernateProxy){
Element child = (Element) ((HibernateProxy) p).getHibernateLazyInitializer()
.getImplementation();
if (child instanceof ElementTypeOne){
//You can cast your object or do whatever you want, knowing for sure that's a child element)
ElementTypeOne myRealElement = (ElementTypeOne) child;
...
} else {
//It should be ElementTypeTwo (if u never create parent entities)
...
}
}
}
)