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

如果你试图在一个实体和一个集合或java对象的列表(例如长类型)之间有一个关系，它会像这样:

@ElementCollection(fetch = FetchType.EAGER)
    public List<Long> ids;

2015-08-24 14:50:11

其他回答

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

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

最好的解决方案之一是在应用程序中添加以下内容。属性文件: spring.jpa.properties.hibernate.enable_lazy_load_no_trans = true

2018-08-01 23:24:38

对于这个惰性初始化问题有多种解决方案

1)将关联Fetch类型从LAZY更改为EAGER，但这不是一个好的做法，因为这会降低性能。

2)使用FetchType。在关联对象上使用LAZY，并在您的服务层方法中使用Transactional注释，以便会话保持打开状态，并且当您调用topicById.getComments()时，子对象(注释)将被加载。

3)另外，在控制器层请尽量使用DTO对象而不是实体。在你的例子中，会话在控制器层被关闭。所以最好在服务层将实体转换为DTO。

2020-04-02 09:24:57

@Controller
@RequestMapping(value = "/topic")
@Transactional

我通过添加@Transactional来解决这个问题，我认为这可以使会话打开

2016-12-14 11:02:20

如何解决“惰性初始化角色集合失败”Hibernate异常

推荐文章

最新文章

标签