所以，我有一个实体，比如说Entity1，它与另一个实体Entity2 结合在一起。Entity2 又与另一个实体Enitity3 连接。
我有 Entity1.entity2 作为OneToMany加入，因此返回一个列表。在 Entity2.entity3 中也是如此，它也是OneToMany并返回一个 List。
现在我正在构建一个 Web 服务，我在其中调用 Enitity1 然后我加载 entity2 (i.e. List<Entity2> entity2 = entity1.getEntity2())。
对于每个 entity2 我加载 entity3(i.e. List<Entity3> entity3 = entity2.getEntity3())
它第一次正确运行查询，但是当它试图Entity3退出时entity2 (i.e. List<Entity3> entity3 = enity2.get(1).getEntity3())会抛出上面提到的异常：
Caused by: javax.persistence.PersistenceException: org.hibernate.HibernateException: collection is not associated with any session
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1179)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1112)
at org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:245)
at com.test.test.adapter.impl.TestDbAdapterImpl.getTestList(TestDbAdapterImpl.java:62)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1052)
at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1124)
at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:5388)
at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:619)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:571)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doAround(SystemInterceptorProxy.java:162)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:144)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:861)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800)
at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:370)
at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:5360)
at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:5348)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:214)
... 86 more