我在加载某些对象时遇到了一个奇怪的问题。我使用的是JPA 1,hibernate-core版本3.3.0.SP1和hibernate-entitymanager版本3.4.0.GA
让我们说这些JPA实体:
@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> {
...
}
问题是,当我加载这些实体的集合时,我想总是获得子类(意思是ElementTypeOne,ElementTypeTwo而不是元素)。问题是多对多的关系总是得到元素(父亲而不是孩子)
让我们说我是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;
如果我收到集合,一切正常(我得到了预期的子类)。
问题来自于我的另一个实体B带有JpaMany3ManyEntity的集合(请注意涉及相同的实体元素)
@OneToMany(cascade = CascadeType.ALL, mappedBy = JpaMany3ManyEntity.ASOCIATION_OVERRIDE_ONE, fetch = FetchType.LAZY)
private Collection<ThreeElementExample> threeElementExampleCollection;
如果我在尝试从类A获取elementCollection之前从类B循环threeElementExampleCollection,那么当我从elementCollection加载对象时 我只获得超类(Element)对象而不是子对象。
我想,无论出于何种原因,多对多关系总是获得Element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。
任何想法或工作环境?任何形式的帮助都会非常感激。
提前致谢。
编辑:多对多的课程:
@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;
...
}
答案 0 :(得分:3)
这是一个对我有用的工作场所:Deproxy the entities。
即使拥有该实体的父代理(jpa.inheritance.issue.Element _ $$ _ javassist_1),如果您将其删除,您将获得真实实体(子代)。
假设您想要从实体A循环您的(子)元素集合并使用它们执行某些操作。
类似的东西:
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)
...
}
}
}
)
它总会像我期待的那样得到儿童元素。
答案 1 :(得分:0)
尝试使用hibernate.default_batch_fetch_size
属性进行试验。默认情况下,它设置为1.这将仅从您的集合中加载第一个实体。将它增加到集合的大小可能会有所帮助。