Spring Hibernate Lazy Fetch集合事务无法正常工作

我完全糊涂了,我一直用hibernate创建我的第一个Spring应用程序,当我从数据库中延迟加载对象时,我似乎无法发现我的错误.

我的模型如下

团队课

@Entity
public class Team {

    @Id
    @Column
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;
    @Column
    private String name;
    @Column
    private String description;

    @OneToMany(fetch=FetchType.LAZY , cascade = CascadeType.ALL, mappedBy="team")
    @JsonIgnore
    public List members;

    //Constructors and setters getters ommited
}

人类

@Entity
@Table(name="`person`")
public class Person {

    @Id
    @Column
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int id;
    @Column
    private String name;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="team")
    @JsonIgnore
    private Team team;

    //omitted constructor and methods
}

然后我有我的数据访问对象,它们都遵循相同的模式

@Repository
public class TeamDaoImpl implements TeamDao {

    @Autowired
    private SessionFactory session;

    @Override
    public void add(Team team) {
        session.getCurrentSession().save(team);
    }

    @Override
    public void edit(Team team) {
        session.getCurrentSession().update(team);
    }

    @Override
    public void delete(int teamId) {
        session.getCurrentSession().delete(getTeam(teamId));
    }

    @Override
    public Team getTeam(int teamId) {
        return (Team) session.getCurrentSession().get(Team.class, teamId);
    }

    @Override
    public List getAllTeam() {
        return session.getCurrentSession().createQuery("from Team").list();
    }

}

在所有这些方法中,我确保使用当前会话来执行这些操作.根据我的理解,这可以确保它将这些调用放入服务类中创建的现有事务中,如下所示:

@Service
public class PersonServiceImpl implements PersonService {

    Logger log = Logger.getLogger(PersonServiceImpl.class);

    @Autowired
    PersonDao personDao;

    @Autowired
    TeamDao teamDao;

    //Ommitted other methods

    @Transactional
    public List getPeopleForTeam(int teamId) {
        log.info("Getting people for team with id " + teamId);
        Team team = teamDao.getTeam(teamId);
        return team.getMembers();
    }

}

我的理解是@Transactional注释应该将该方法放入单个事务中.

这一切都很好编译,但是当我运行它时,我得到以下错误

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: model.Team.members, no session or session was closed; nested exception is 
com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: model.Team.members, no session or session was closed
    org.springframework.http.converter.json.MappingJackson2HttpMessageConverter.writeInternal(MappingJackson2HttpMessageConverter.java:207)     

org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:179)    

org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:148)  
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:90)   
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:189)     
org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:69)     
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:122)     
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:745)    
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)    
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)    
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)    
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)     
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)  
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)   
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)    
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)     
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)    
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)

我究竟做错了什么？我对@Transactional注释的理解是不正确的？如果是这样,我应该如何在对象内部进行延迟加载集合,并在某些事务方法中获取它们？

编辑:

这是我弹簧配置的相关部分

 
        
        
            classpath:hibernate.cfg.xml
        
        
            org.hibernate.cfg.AnnotationConfiguration
        
        
            
                ${jdbc.dialect}
                true
            
        
  

  
            
             

这是配置的另一部分

这是控制器的一部分

@RequestMapping(value="/{teamId}/people", method=RequestMethod.GET)
    public @ResponseBody List getPeopleForTeam(@PathVariable int teamId) {
        return personService.getPeopleForTeam(teamId);
    }

Evgeni Dimit.. 13

您可能从控制器调用服务方法(例如).怎么了:

-controller method
    -call service method
        -start transaction
              -hibernate do lazy loading
        -end transaction
    -end service method
    you try to access somethind from the lazy initialied list, but no hibernate transaction    here
-end controller method

延迟加载意味着hibernate有一个代理对象,它只存储实体的id,只在需要时执行select语句(例如访问实体的某些属性).你可以看看,Open session in view但它被认为是不好的做法为什么Hibernate Open Session in View被认为是一种不好的做法？.尝试急切地获取集合.

编辑:1)Hibernate要求在事务中执行所有操作,例如

Transaction tx = null;
      try{
         tx = session.beginTransaction();
         ...
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }

2)延迟加载:Hibernate创建代理对象(它不会向DB发送语句).当您尝试访问代理时,会向数据库发送一条语句并返回结果(这需要在休眠事务处理中.)

3)Spring通过使用AOP拦截给定方法来简化事务管理.首先,它启动一个事务,然后调用该方法并提交或回滚它.

getPeopleForTeam()返回代理.然后在事务之外的某个地方访问某些属性,而hibernate尝试触发select语句.