如何解决“未能懒散地初始化角色集合”的Hibernate异常 [英] How to solve the “failed to lazily initialize a collection of role” Hibernate exception
问题描述
我遇到了这个问题：
org.hibernate.LazyInitializationException：懒得初始化角色集合：mvc3.model.Topic .comments，没有会话或会话关闭
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: mvc3.model.Topic.comments, no session or session was closed
以下是模型：
@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;
}
}
控制器，调用模型外观如下所示：
The controller, which calls model looks like the following:
@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：
The jsp-page looks li the following:
<%@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时出现例外异常。在 c：forEach 循环的行中
Exception is rised, when viewing jsp. In the line with c:forEach loop
推荐答案
如果你知道你想要看到所有评论每次检索主题然后更改评论的字段映射 to：
If you know that you'll want to see all Comments every time you retrieve a Topic then change your field mapping for comments to:
@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，请看这个。
Collections are lazy-loaded by default, take a look at this if you want to know more.
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