JSF / EJB3避免了视图层中的延迟初始化异常(JSF / EJB3 avoiding lazy initialization exceptions in the view layer)

 我有以下JSF / PrimeFaces EJB架构： 
 
 [JSF / PrimeFaces xhtml视图] - > [@ManagedBean JSF bean] - > [@Stateless EJB3 bean] --JPA - > [DB] 
 
 也就是说，JSF视图显示它们在其支持bean（ @ManagedBean ）上访问的实体和集合，并且这些集合和实体依次通过调用注入了EntityManager的无状态EJB3 “facade”bean来获取，并使用JPA支持来访问数据库。 休眠 。 无状态EJB3 bean也提供了一些服务，但在大多数情况下，它们的作用是根据需要显示它们的xhtml视图的请求，从数据库中提供Entity对象（ JPA -annotated）。 
 
 现在就是这样：如果我的理解是正确的，那么当无状态EJB3 bean返回Entity bean时，它们会在每个EJB3 bean方法划分事务时分离。 通常情况是，当xhtml视图和JSF Managed bean导航如此获取的Entity对象的图形（One-To-Many集合等）时，我经常得到如下的Lazy Initialization异常： 
 
javax.el.ELException: ... org.hibernate.LazyInitializationException: failed
to lazily initialize a collection of role: ..., no session or session was closed
 
 唯一有效的是将集合更改为EAGER -ly加载，但这不是一个实用的解决方案。 当分离的JPA实体找到进入视图层的方式时，要使用哪些好的模式，以避免一劳永逸的延迟初始化异常，而不是必须以临时方式处理每个案例？ 

I have the following JSF/PrimeFaces EJB architecture:
 
[JSF/PrimeFaces xhtml view] --> [@ManagedBean JSF bean] --> [@Stateless EJB3 bean] --JPA--> [DB]
 
That is, the JSF views display entities and collections they access on their backing beans (@ManagedBean) and these collections and entities are in turn fetched by calling stateless EJB3 "facade" beans that have the EntityManager injected and access the database using JPA backed by Hibernate. The stateless EJB3 beans also provide some services but for the most part their role is to provide the Entity objects (JPA-annotated) from the database, as requested by the xhtml views that need to display them.
 
Now here's the thing: if my understanding is correct, the moment the Entity beans are returned by the stateless EJB3 beans, they become detached as each EJB3 bean method demarcates a transaction. It is then often the case that as the xhtml views and the JSF Managed beans navigate the graphs of the Entity objects so fetched (One-To-Many collections and such), I often get Lazy Initialization exceptions like the following:
 
javax.el.ELException: ... org.hibernate.LazyInitializationException: failed
to lazily initialize a collection of role: ..., no session or session was closed
 
The only thing that works is changing collections to be EAGER -ly loaded but that's not a pragmatic solution. What are some good patterns to use when detached JPA entity find their way to the view layer in order to avoid once and for all the lazy initialization exceptions rather than having to treat each case in an ad-hoc manner?

原文：https://stackoverflow.com/questions/13089888