如何解决“惰性初始化角色集合失败”Hibernate异常

我有这样一个问题:

org.hibernate.LazyInitializationException:惰性初始化role: mvc3.model.Topic.comments集合失败，没有会话或会话已关闭

下面是模型:

@Entity
@Table(name = "T_TOPIC")
public class Topic {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;

    @ManyToOne
    @JoinColumn(name="USER_ID")
    private User author;

    @Enumerated(EnumType.STRING)    
    private Tag topicTag;

    private String name;
    private String text;

    @OneToMany(mappedBy = "topic", cascade = CascadeType.ALL)
    private Collection<Comment> comments = new LinkedHashSet<Comment>();

    ...

    public Collection<Comment> getComments() {
           return comments;
    }

}

调用model的控制器如下所示:

@Controller
@RequestMapping(value = "/topic")
public class TopicController {

    @Autowired
    private TopicService service;

    private static final Logger logger = LoggerFactory.getLogger(TopicController.class);


    @RequestMapping(value = "/details/{topicId}", method = RequestMethod.GET)
    public ModelAndView details(@PathVariable(value="topicId") int id)
    {

            Topic topicById = service.findTopicByID(id);
            Collection<Comment> commentList = topicById.getComments();

            Hashtable modelData = new Hashtable();
            modelData.put("topic", topicById);
            modelData.put("commentList", commentList);

            return new ModelAndView("/topic/details", modelData);

     }

}

jsp页面看起来如下所示:

<%@page import="com.epam.mvc3.helpers.Utils"%>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page session="false" %>
<html>
<head>
      <title>View Topic</title>
</head>
<body>

<ul>
<c:forEach items="${commentList}" var="item">
<jsp:useBean id="item" type="mvc3.model.Comment"/>
<li>${item.getText()}</li>

</c:forEach>
</ul>
</body>
</html>

在查看jsp时，将引发异常。在c:forEach循环的行中

当前回答

对于fetch = FetchType.LAZY，你应该有两个东西。

@Transactional

and

Hibernate.initialize(topicById.getComments());

2019-10-05 03:54:15

其他回答

为了解决这个问题，在我的例子中，它只是少了这一行

<tx:annotation-driven transaction-manager="myTxManager" />

在应用程序上下文文件。

方法上的@Transactional注释没有考虑在内。

希望这个答案能帮助到一些人

2016-02-05 16:02:59

在我的情况下，下面的代码是一个问题:

entityManager.detach(topicById);
topicById.getComments() // exception thrown

因为它从数据库中分离，当需要时Hibernate不再从字段中检索list。所以我在分离之前初始化它:

Hibernate.initialize(topicById.getComments());
entityManager.detach(topicById);
topicById.getComments() // works like a charm

2017-01-27 14:03:12

此问题是由于在关闭hibernate会话的情况下访问属性造成的。控制器中没有hibernate事务。

可能的解决方式:

Do all this logic, in the service layer, (with the @Transactional), not in the controller. There should be the right place to do this, it is part of the logic of the app, not in the controller (in this case, an interface to load the model). All the operations in the service layer should be transactional. i.e.: Move this line to the TopicService.findTopicByID method: Collection commentList = topicById.getComments(); Use 'eager' instead of 'lazy'. Now you are not using 'lazy' .. it is not a real solution, if you want to use lazy, works like a temporary (very temporary) workaround. use @Transactional in the Controller. It should not be used here, you are mixing service layer with presentation, it is not a good design. use OpenSessionInViewFilter, many disadvantages reported, possible instability.

一般来说，最佳解是1。

2017-02-13 14:17:16

原因是你试图在关闭服务内的会话后在你的控制器上获得commentList。

topicById.getComments();

只有当您的休眠会话处于活动状态时，上面才会加载commentList，我猜您在服务中关闭了休眠会话。

因此，您必须在关闭会话之前获得commentList。

2018-03-16 10:11:10

对于那些使用Criteria的人，我发现

criteria.setFetchMode("lazily_fetched_member", FetchMode.EAGER);

我该做的都做了

集合的初始获取模式设置为FetchMode。LAZY提供性能，但当我需要数据时，我只需要添加这一行，并享受完全填充的对象。

2015-12-01 05:22:43

如何解决“惰性初始化角色集合失败”Hibernate异常

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