解决“未能懒惰地初始化角色集合”例外 [英] Solve "failed to lazily initialize a collection of role" exception
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问题描述
我有这个问题：
org.hibernate.LazyInitializationException：无法延迟初始化角色集合：mvc3.model.Topic
以下是模型：
< pre $
@Entity
@Table（name =T_TOPIC）
public class Topic {
@Id
@GeneratedValue （strategy = GenerationType.AUTO）
private int id;
@ManyToOne
@JoinColumn（name =USER_ID）
私人用户作者;
@Enumerated（EnumType.STRING）
私有标签topicTag;
私人字符串名称;
私人字符串文本;
@OneToMany（mappedBy =topic，cascade = CascadeType.ALL）
private Collection< Comment> comments = new LinkedHashSet< Comment>（）;
...
公开收藏<评论> getComments（）{
返回评论;
$ b 调用模型外观的控制器如下所示：
@Controller
@RequestMapping（value =/ topic）
public class TopicController {
@Autowired
私人TopicService服务;
private static final Logger logger = LoggerFactory.getLogger（TopicController.class）;
@RequestMapping（value =/ details / {topicId}，method = RequestMethod.GET）
public ModelAndView详细信息（@PathVariable（value =topicId）int id）
{
主题topicById = service.findTopicByID（id）;
收藏<评论> commentList = topicById.getComments（）;
Hashtable modelData = new Hashtable（）;
modelData.put（topic，topicById）;
modelData.put（commentList，commentList）;
返回新的ModelAndView（/ topic / details，modelData）;
}
}
jsp-
<％@ page import =com.epam.mvc3.helpers.Utils％> ;
<％@ page language =javacontentType =text / html; charset = UTF-8pageEncoding =UTF-8％>
<％@ taglib uri =http://java.sun.com/jsp/jstl/coreprefix =c％>
<％@ page session =false％>
< html>
< head>
< title>查看主题< / title>
< / head>
< body>
< ul>
< c：forEach items =$ {commentList}var =item>
< jsp：useBean id =itemtype =mvc3.model.Comment/>
< li> $ {item.getText（）}< / li>
< / c：forEach>
< / ul>
< / body>
< / html>
查看jsp时异常升级。符合 c：forEach 循环
解决方案
如果您知道您希望看到所有评论 s每当您检索主题时，请更改评论的字段映射 code>到：
@OneToMany（fetch = FetchType.EAGER，mappedBy =topic，cascade = CascadeType。全部）
私人收藏<评论> comments = new LinkedHashSet< Comment>（）;
默认情况下，集合是延迟加载的，请查看这，如果你想知道更多。
I have this problem:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: mvc3.model.Topic.comments, no session or session was closed
Here is the model:
@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;
}
}
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);
}
}
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>
Exception is rised, when viewing jsp. In the line with c:forEach loop
解决方案
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>();
Collections are lazy-loaded by default, take a look at this if you want to know more.
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