如何解决“无法延迟初始化角色集合”的Hibernate异常

  • Z时代
  • 2024-01-10
  • 分类：问答

我有这个问题：

org.hibernate.LazyInitializationException：无法延迟初始化角色集合：mvc3.model.Topic.comments，没有会话或会话被关闭

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>

查看jsp时会引发异常。与c：forEach循环一致

回答：

如果你知道Comment每次检索a时都希望看到全部，Topic则将字段映射更改为comments：

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

默认情况下，集合是延迟加载的。

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