休眠，JPA - 例子manytomany与两个表

Question

我尝试使用多对多的集合映射，我有两个表： TASK和TASKRELATED，每个任务可以有许多相关的任务，每个相关的任务可以在许多父任务。这里是我的SQL图：

这里是我的实体：

@Entity 
public class Task { 

    @Id 
    @GeneratedValue(strategy=GenerationType.IDENTITY) 
    private Long taskId; 

    @ManyToMany 
    @JoinTable(name = "taskRelated", joinColumns = { @JoinColumn(name = "relatedTaskId") }, inverseJoinColumns = { @JoinColumn(name = "taskId") }) 
    private Set<Task> relatedTasks = new HashSet<Task>(0); 

} 

这里是我的ropository：

public interface ITaskRepository extends JpaRepository<Task, Long>, 
    QueryDslPredicateExecutor<Task>{ 
} 

这是我的代码：

Task t = repository.findOne(1L); 

这是我的数据在MySQL： 任务表

taskrelated表

当我做阅读任务对象的，有恩的错误：

failed to lazily initialize a collection of role: org.Task.relatedTasks, no session or session was closed 
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: org.Task.relatedTasks, no session or session was closed 
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:383) 
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:375) 
    at org.hibernate.collection.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:122) 
    at org.hibernate.collection.PersistentSet.size(PersistentSet.java:162) 
    at com.github.springtestdbunit.sample.service.UsersServiceTest.testTask(UsersServiceTest.java:63) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
    at java.lang.reflect.Method.invoke(Method.java:601) 
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44) 
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) 
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41) 
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20) 
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74) 
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83) 
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72) 

请帮帮忙！

在@ManyToMany(fetch=FetchType.EAGER)情况下，有错误是这样的：

illegal access to loading collection 
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.PersistentSet.hashCode(PersistentSet.java:434) 
    at org.Task.hashCode(Task.java:36) 
    at java.util.HashMap.hash(HashMap.java:351) 
    at java.util.HashMap.put(HashMap.java:471) 
    at java.util.HashSet.add(HashSet.java:217) 
    at java.util.AbstractCollection.addAll(AbstractCollection.java:334) 
    at org.hibernate.collection.PersistentSet.endRead(PersistentSet.java:352) 
    at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollection(CollectionLoadContext.java:261) 
    at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:246) 
    at org.hibernate.engine.loading.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:219) 
    at org.hibernate.loader.Loader.endCollectionLoad(Loader.java:1005) 
    at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:993) 

Answer 1

它不能初始化集合，你试图将设定的没有初始化它？：

@ManyToMany 
@JoinTable(name = "taskRelated", joinColumns = { @JoinColumn(name = "relatedTaskId") }, inverseJoinColumns = { @JoinColumn(name = "taskId") }) 
private Set<Task> relatedTasks; 

Answer 2

由于异常说你正在尝试访问关闭会话后的收集元素 - relatedTasks，Hibernate默认情况下会延迟加载收集元素。

所以，你需要在会​​话中访问的元素或者你也可以抓取类型添加到EAGER

@ManyToMany(fetch = FetchType.EAGER) 

更新：

按堆栈跟踪异常 - LazyInitializationException: illegal access to loading collection它具有：

at org.hibernate.collection.PersistentSet.hashCode(PersistentSet.java:434) 
at org.nli.seoweb.domain.Task.hashCode(Task.java:36) 

基于此，我假设你已经覆盖了hashCode方法Task实体，该方法尝试访问Set。至于Hibernate提供了Set这是PersistentSet在这种情况下，包装类，调用hashCode()内部有一个检查，如果Set被完全初始化，然后抛出该异常验证。

因此，请尝试修改您的Task.hashCode()方法，并确保您没有使用其中的Set，并确定它是否解决了问题。

您也可以参考this post类似的例外。