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

@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

其他回答

在第二次执行生成JWT令牌的方法后，我得到了这个错误。

line user.getUsersRole().stream().forEachOrdered((ur) -> roles.add(ur. getroleid ()));生成错误。

// MyUserDetails.java

@Service
public class MyUserDetails implements UserDetailsService {

  @Override
  public UserDetails loadUserByUsername(String email) {

    /* ERROR
    /* org.hibernate.LazyInitializationException: failed to 
    /* lazily initialize a collection of role: 
    /* com.organizator.backend.model.User.usersRole, 
    /* could not initialize proxy - no Session */
    user.getUsersRole().stream().forEachOrdered((ur) ->
           roles.add(ur.getRoleId()));

在我的例子中，@Transactional注释解决了它，

// MyUserDetails.java

import org.springframework.transaction.annotation.Transactional;

@Service
public class MyUserDetails implements UserDetailsService {

  @Override
  @Transactional // <-- added
  public UserDetails loadUserByUsername(String email) {

    /* No Error */
    user.getUsersRole().stream().forEachOrdered((ur) ->
           roles.add(ur.getRoleId()));

2021-09-05 13:51:18

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

在我的Spring-Boot项目中，spring.jpa.open-in-view在application.properties中被设置为false。将其设置为true就解决了这个问题。

2021-12-27 17:43:30

如果你知道你想在每次检索主题时看到所有的注释，那么将注释的字段映射更改为:

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

默认情况下，集合是惰性加载的，如果你想了解更多，可以看看这个。

2012-07-31 18:33:08

在我的情况下，下面的代码是一个问题:

entityManager.detach(topicById);
topicById.getComments() // exception thrown

因为它从数据库中分离，当需要时Hibernate不再从字段中检索list。所以我在分离之前初始化它:

Hibernate.initialize(topicById.getComments());
entityManager.detach(topicById);
topicById.getComments() // works like a charm

2017-01-27 14:03:12

如何解决“惰性初始化角色集合失败”Hibernate异常

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