Question

我尝试使用多对多的集合映射，我有两个表： TASK和TASKRELATED，每个任务都可以有许多相关任务，每个相关任务都可以在许多父任务中完成。这是我的sql图：

enter image description here

这是我的实体：

@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);

这是我在mysql中的数据：任务表
enter image description here
任务相关表

当我读取任务对象时，出现错误：

    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)

请帮忙！

如果@ManyToMany(fetch=FetchType.EAGER)，则会出现如下错误：

 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

它无法初始化集合，您是否尝试在不初始化的情况下添加集合？：

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

Answer 2

正如异常所说，你试图在关闭会话后访问集合元素 - relatedTasks，并且Hibernate默认会懒洋洋地加载集合元素。

因此您需要访问会话中的元素，或者您可以将获取类型添加到EAGER

 @ManyToMany(fetch = FetchType.EAGER)

<强>更新

根据异常的stacktrace - LazyInitializationException: illegal access to loading collection它有：

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

基于此，我假设您已覆盖hashCode实体中的Task方法，此方法正尝试访问Set。由于Hibernate在这种情况下为Set提供了PersistentSet的包装类，因此在内部调用hashCode()进行验证，检查Set是否已完全初始化，然后抛出异常。

因此，请尝试修改您的Task.hashCode()方法，并确保您没有使用Set，并查看它是否解决了问题。

您也可以参考this post获取类似的例外情况。

Hibernate，JPA - 示例manytomany有两个表

2 个答案: