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java - 如何解决Hibernate异常 “failed to lazily initialize a collection of role”

转载 作者：行者123 更新时间：2023-12-02 01:50:37 25 4
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我有这个问题:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: mvc3.model.Topic.comments, no session or session was closed

这是模型:

@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;
    }

}

调用模型的 Controller 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>

查看jsp时出现异常。在带有 c:forEach 循环的行

最佳答案

如果您知道每次检索主题时都希望看到所有评论，请更改评论的字段映射至:

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

集合默认是延迟加载的，看看this如果您想了解更多。

关于java - 如何解决Hibernate异常 “failed to lazily initialize a collection of role”，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57429223/

25 4 0
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