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[英]LazyInitializationException even though @Transactional is used
[英]LazyInitializationException even with @Transactional
当我去获取用户的评论时,很难让 ManyToOne 实体映射的简单 OneToMany 工作。 其他答案建议您必须使用 entityManager 自己创建查询,但这似乎太可怕了。 如果没有硬编码内联 sql 就不能做这样简单的事情,那么 ORM 的意义何在? 似乎我做错了什么的可能性更大。
似乎这可能与我使用模型从 jsp 访问 user.getComments() 方法这一事实有关。 不确定这样做的最佳方法是什么。
架构:
CREATE TABLE users (
id INTEGER AUTO_INCREMENT PRIMARY KEY,
username VARCHAR(255) UNIQUE NOT NULL,
created_at TIMESTAMP DEFAULT NOW()
);
CREATE TABLE comments (
id INTEGER AUTO_INCREMENT PRIMARY KEY,
comment_text VARCHAR(255) NOT NULL,
photo_id INTEGER NOT NULL,
user_id INTEGER NOT NULL,
created_at TIMESTAMP DEFAULT NOW(),
FOREIGN KEY(user_id) REFERENCES users(id)
);
用户控制器方法:
@RequestMapping("/user")
public ModelAndView getUser(@RequestParam int id) {
return new ModelAndView("user", "message", userService.getUser(id));
}
用户服务:
@Service
public class UserService {
private UserDAO userDAO;
@Autowired
public UserService(UserDAO userDAO) {
this.userDAO = userDAO;
}
@Transactional
public User getUser(int id) {
return userDAO.getUser(id);
}
}
用户DAO:
@Repository
public class UserDAO {
@PersistenceContext
EntityManager entityManager;
@Nullable
public User getUser(int id)
{
return entityManager.find(User.class, id);
}
}
用户实体:
@Entity
@Table(name="users")
public class User {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="id")
private int id;
@Column(name="username")
private String userName;
@Temporal(TemporalType.TIMESTAMP)
@Column(name="created_at")
private Date createdAt;
@OneToMany(mappedBy="user")
private List<Comment> comments;
public int getId() {
return id;
}
public String getUserName() {
return userName;
}
public Date getCreatedAt() {
return createdAt;
}
@Transactional
public List<Comment> getComments() {
return comments;
}
}
评论实体:
@Entity
@Table(name="comments")
public class Comment {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
@Column(name="id")
private int id;
@Column(name="comment_text")
private String commentText;
@Column(name="photo_id")
private int photoId;
@ManyToOne
@JoinColumn(name="user_id")
private User user;
@Temporal(TemporalType.TIMESTAMP)
@Column(name = "created_at")
private Date createdAt;
@Override
public String toString() {
return "Comment [id=" + id + ", commentText=" + commentText + ", photoId=" + photoId + ", userId=" + user.getId()
+ ", createdAt=" + createdAt + "]";
}
public int getId() {
return id;
}
public String getCommentText() {
return commentText;
}
public int getPhotoId() {
return photoId;
}
public User getUser() {
return user;
}
public Date getCreatedAt() {
return createdAt;
}
}
堆栈跟踪:
严重:servlet [dispatcher] 的 Servlet.service() 在路径 [/test] 的上下文中抛出异常 [在第 [34] 行处理 [WEB-INF/jsp/user.jsp] 时发生异常
31:用户 32:创建日期 33:34:35:36:37:
Stacktrace:] 与根本原因 org.hibernate.LazyInitializationException: 未能延迟初始化角色集合:com.instagramviewer.entity.User.comments,无法初始化代理 - 在 org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException 没有会话(AbstractPersistentCollection.java:602) 位于 org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:217) 位于 org.hibernate.collection.internal.AbstractPersistentCollection.java:217. collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:148) at org.hibernate.collection.internal.PersistentBag.iterator(PersistentBag.java:303) at org.apache.taglibs.standard.tag.common.core.ForEachSupport。 toForEachIterator(ForEachSupport.java:348) 在 org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.jav a:224) 在 org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:155) 在 javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:256)在 org.apache.jsp.WEB_002dINF.jsp.user_jsp._jspx_meth_c_005fforEach_005f0(user_jsp.java:285) 在 org.apache.jsp.WEB_002dINF.jsp.user_jsp._jspService(user_jsp._jsp) 在 org.apache.jsp._jspService(user_jsp._jsp.java: .HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:476) at org. apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385) 在 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329) 在 javax.servlet.http.HttpServlet.service(HttpServlet.java: 741) 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) 在 org.apache.tomcat.websocke t.server.WsFilter.doFilter(WsFilter.java:53) 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java: 166) 在 org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) 在 org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) 在 org.apache.catalina.core.ApplicationDispatcher .doForward(ApplicationDispatcher.java:384) at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:170) org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:316) 在 org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1370) 在 org.springframework.web.servlet.DispatcherServlet。 processDispatchResult(DispatcherServlet.java:1116) a t org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055) 在 org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) 在 org.springframework.web.servlet.FrameworkServlet.processRequest (FrameworkServlet.java:1005) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) at org.springframework.web。 servlet.FrameworkServlet.service(FrameworkServlet.java:882) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org .apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) 在 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) 在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter (ApplicationFilterChain.java:193) 在 org.apache.catalina.core.ApplicationFilterChain.do Filter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache .catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(javaReference) :92) 在 org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:668) 在 org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) 在 org.apache.catalina.connector. CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache .coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834) 在 org.apache.tomcat.util.n et.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415) 在 org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java: 1149) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) 在 org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) 在 java.lang.Thread .run(Thread.java:748)
@Vlad 已经注意到,您在交易之外引用Comment
。 由于您使用的是 jpql,您可以急切地获取User
及其评论:
public List<User> getAllUsers()
{
TypedQuery<User> query = entityManager.createQuery("SELECT e from User e left join fetch e.comments", User.class);
return (List<User>) query.getResultList();
}
我做错了两件事:
第一:我忘记在我的 spring java 配置类中启用事务管理
@Configuration
@EnableTransactionManagement
public class AppConfig {
@Bean
public LocalContainerEntityManagerFactoryBean factoryBean() {
LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
factory.setPersistenceProviderClass(HibernatePersistenceProvider.class);
return factory;
}
@Bean
public PlatformTransactionManager transactionManager(){
JpaTransactionManager transactionManager = new JpaTransactionManager();
transactionManager.setEntityManagerFactory(factoryBean().getObject() );
return transactionManager;
}
}
第二:正如 Vlad 所说,我需要在我的服务层中将评论列表初始化为事务的一部分
@Transactional
public User getUser(int id) {
User user = userDAO.getUser(id);
Hibernate.initialize(user.getComments());
return user;
}
现在我可以避免使用 join fetch 解决方案,这只会在我想要检索评论列表的服务层中的任何位置添加一行 java 代码。
@Transactional
对您没有帮助,因为当您尝试加载评论(在 JSP 级别)时,事务已经关闭(它在getUser
方法开始时打开并在完成时关闭)。 可能的方法是在事务中初始化您的评论。
@Transactional
public User getUser(int id) {
User user = userDAO.getUser(id);
user.getComments().size(); //initializing
return user;
}
这是最原始的方式,但应该适合你。 如果它有效,您可以稍后阅读有关Named Entity Graph
。 这是初始化所需惰性关联的更高级方法。
我试图从一开始就避免这样做,但我想保持实体的 fetch 类型懒惰的最佳方法是在 DAO 层中创建一个使用 join fetch 急切地获取的方法。
@Nullable
public User getUser(int id)
{
TypedQuery<User> query = entityManager.createQuery("SELECT e from User e left join fetch e.comments c where e.id = :id", User.class);
query.setParameter("id", id);
return query.getSingleResult();
}
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