[英]Inheritance JPA and Hibernate Issue
我加載一些對象時遇到了一個奇怪的問題。 我正在使用JPA 1,hibernate-core版本3.3.0.SP1和hibernate-entitymanager版本3.4.0.GA
假設我有這些JPA實體:
@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> {
...
}
問題是,當我加載這些實體的集合時,我想總是獲得子類(意思是ElementTypeOne,ElementTypeTwo而不是元素)。 問題是多對多的關系總是得到元素(父親而不是孩子)
假設我有一個包含元素集合的實體A:
@Fetch(FetchMode.JOIN)
@OneToMany(cascade = CascadeType.ALL, mappedBy = "idEle")
private Collection<Element> elementCollection;
如果我得到了集合,一切正常(我得到了預期的子類)。
當我有另一個帶有JpaMany3ManyEntity集合的實體B時出現問題(注意涉及相同的實體元素)
@OneToMany(cascade = CascadeType.ALL, mappedBy = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_ONE, fetch = FetchType.LAZY)
private Collection<ThreeElementExample> threeElementExampleCollection;
如果我在嘗試從類A獲取elementCollection之前從類B循環threeElementExampleCollection,當我從elementCollection加載對象時,我只獲取超類(Element)對象而不是子對象。
我想,無論出於何種原因,多對多關系總是獲得Element對象(父對象)並將它們保存在hibernate緩存中,但我需要避免這種行為。
任何想法或workarround? 任何形式的幫助將非常感激。
提前致謝。
編輯:多對多班:
@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;
...
}
這是一個對我有用的工作場所:Deproxy實體。
即使擁有該實體的父代理(jpa.inheritance.issue.Element _ $$ _ javassist_1),如果您將其刪除,您將獲得真實實體(子代)。
假設您想要從實體A循環您的(子)元素集合並使用它們執行某些操作。
就像是:
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)
...
}
}
}
)
它將始終像我期待的那樣獲得兒童元素。
嘗試使用hibernate.default_batch_fetch_size
屬性進行實驗。 默認情況下,它設置為1.這將僅從您的集合中加載第一個實體。 將它增加到集合的大小可能會有所幫助。
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