如果我的 DataModel 中有双向关系,我的应用程序有责任在 java 代码中保持引用是最新的。
做这个的最好方式是什么?
例如比迪尔。A 和 B 之间的 1:N 关系。
@Entity
class A {
@ManyToOne
private B b;
}
@Entity
class B {
@OneToMany(mappedBy="b")
private Collection<A> as;
}
如果我说 B.addA(b) 这不会让 A 中的变量 b 指向我添加的引用。如果我调用 A.setB(b) 这不会将 b 的引用添加到 B 中的集合。
一种可能的方法是在我的应用程序代码中调用 setB 和 addA。
另一种可能性是像这样编写 setA(..) 方法:
public setB(B b) {
this.b = b;
if(!b.contains(this) {
b.add(this);
}
}
public addA(A a) {
if(!as.conatains(a)) {
as.add(a);
}
a.setB(this);
}
但这有时会引发一些异常,例如:
org.hibernate.LazyInitializationException: illegal access to loading collection
我猜是因为框架在某个时候调用了这个 setMethod 并想要加载“this”引用......?!?有人可以解释一下为什么会这样吗?有什么方法可以保证我的 java 代码中有干净的双向关系?
谢谢
更新:这是原始代码:
@Entity
class Cluster{
private Grid grid
//someother fields
@ManyToOne
public Grid getGrid() {
return grid;
}
public void setGrid(Grid grid) {
this.grid = grid;
if(!grid.getClusters().contains(this)) { //HERE AN EXCEPTION IS THROWN
grid.addCluster(this);
}
}
}
@Entity
class Grid {
private Collection<Cluster> clusters = new ArrayList<Cluster>();
//some other fields
@OneToMany(mappedBy = "grid", cascade = CascadeType.PERSIST, orphanRemoval = true)
public Collection<Cluster> getClusters() {
return clusters;
}
public void setClusters(Collection<Cluster> clusters) {
this.clusters = clusters;
}
public void addCluster(Cluster c) {
this.clusters.add(c);
c.setGrid(this);
}
}
在我的一个查询中,我得到一个异常,它说 setGrid 方法里面的东西是错误的......如果我删除这些行一切都很好.. 但是我没有我的双向......:/
堆栈跟踪:
Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.PropertyAccessException: Exception occurred inside setter of dst1.model.Cluster.grid
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1214)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1147)
at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:255)
at dst1.Main.dst02b(Main.java:828)
at dst1.Main.main(Main.java:38)
Caused by: org.hibernate.PropertyAccessException: Exception occurred inside setter of dst1.model.Cluster.grid
at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:89)
at org.hibernate.tuple.entity.AbstractEntityTuplizer.setPropertyValues(AbstractEntityTuplizer.java:583)
at org.hibernate.tuple.entity.PojoEntityTuplizer.setPropertyValues(PojoEntityTuplizer.java:229)
at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:3822)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:152)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:982)
at org.hibernate.loader.Loader.doQuery(Loader.java:857)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.loadEntity(Loader.java:2037)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:86)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:76)
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3268)
at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:496)
at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:477)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:285)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:152)
at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1090)
at org.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1038)
at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:630)
at org.hibernate.type.EntityType.resolve(EntityType.java:438)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:139)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:982)
at org.hibernate.loader.Loader.doQuery(Loader.java:857)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.doList(Loader.java:2533)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
at org.hibernate.loader.Loader.list(Loader.java:2271)
at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:452)
at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1268)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:246)
... 2 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:66)
... 35 more
Caused by: org.hibernate.PropertyAccessException: Exception occurred inside setter of dst1.model.Cluster.grid
at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:89)
at org.hibernate.tuple.entity.AbstractEntityTuplizer.setPropertyValues(AbstractEntityTuplizer.java:583)
at org.hibernate.tuple.entity.PojoEntityTuplizer.setPropertyValues(PojoEntityTuplizer.java:229)
at org.hibernate.persister.entity.AbstractEntityPersister.setPropertyValues(AbstractEntityPersister.java:3822)
at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:152)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:982)
at org.hibernate.loader.Loader.doQuery(Loader.java:857)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.loadCollection(Loader.java:2166)
at org.hibernate.loader.collection.CollectionLoader.initialize(CollectionLoader.java:62)
at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:627)
at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:83)
at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1863)
at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:369)
at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:111)
at org.hibernate.collection.AbstractPersistentCollection.readElementExistence(AbstractPersistentCollection.java:167)
at org.hibernate.collection.PersistentBag.contains(PersistentBag.java:262)
at dst1.model.Cluster.setGrid(Cluster.java:114)
... 40 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:66)
... 57 more
Caused by: org.hibernate.LazyInitializationException: illegal access to loading collection
at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:366)
at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:111)
at org.hibernate.collection.AbstractPersistentCollection.readElementExistence(AbstractPersistentCollection.java:167)
at org.hibernate.collection.PersistentBag.contains(PersistentBag.java:262)
at dst1.model.Cluster.setGrid(Cluster.java:114)
... 62 more