以下是一些背景代码:
InitiativeProfileQuestion。java:
@Entity
@Table
public class InitiativeProfileQuestion implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(nullable = false)
private String question;
@Column
private String description;
@Column
private int sortOrder;
@OneToMany(mappedBy = "initiativeProfileQuestion", fetch = FetchType.LAZY)
private List<InitiativeProfileAnswer> answers;
public List<InitiativeProfileAnswer> getAnswers() {
return answers;
}
public void setAnswers(List<InitiativeProfileAnswer> answers) {
this.answers = answers;
}
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getQuestion() {
return question;
}
public void setQuestion(String question) {
this.question = question;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public int getSortOrder() {
return sortOrder;
}
public void setSortOrder(int sortOrder) {
this.sortOrder = sortOrder;
}
}
ProfileAnswer.java:
@Entity
@Table
public class InitiativeProfileAnswer {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column
private String answer;
@Column
private int sortOrder;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "initiativeProfileQuestionId")
@JsonIgnore
private InitiativeProfileQuestion initiativeProfileQuestion;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getAnswer() {
return answer;
}
public void setAnswer(String answer) {
this.answer = answer;
}
public int getSortOrder() {
return sortOrder;
}
public void setSortOrder(int sortOrder) {
this.sortOrder = sortOrder;
}
public InitiativeProfileQuestion getInitiativeProfileQuestion() {
return initiativeProfileQuestion;
}
public void setInitiativeProfileQuestion(InitiativeProfileQuestion initiativeProfileQuestion) {
this.initiativeProfileQuestion = initiativeProfileQuestion;
}
}
InitiativeProfileQuestionRepository。java:
public interface InitiativeProfileQuestionRepository extends JpaRepository<InitiativeProfileQuestion, Long> {
@Query("select ipa from InitiativeProfileQuestion ipa join fetch ipa.answers")
public List<InitiativeProfileQuestion> getAllQuestions();
}
InitiativeProfileService。java:
@Service
public class InitiativeProfileService {
@Autowired
private InitiativeProfileQuestionRepository initiativeProfileQuestionRepository;
public List<InitiativeProfileQuestion> getAllQuestions() {
return initiativeProfileQuestionRepository.findAll();
}
public List<InitiativeProfileQuestion> getAllQuestionsFetch() {
return initiativeProfileQuestionRepository.getAllQuestions();
}
}
基础ontroller.java:
@RestController
@RequestMapping("/api")
public class BaseController {
@Autowired
InitiativeProfileService initiativeProfileService;
@RequestMapping("/question")
public List<InitiativeProfileQuestion> getQuestions() {
return initiativeProfileService.getAllQuestions();
}
@RequestMapping("/questionFetch")
public List<InitiativeProfileQuestion> getQuestionsFetch() {
return initiativeProfileService.getAllQuestionsFetch();
}
}
在我的BaseController中调用get问题()会返回“无法初始化代理-没有会话”错误。但是,在我的BaseController中调用get问卷Fetch()可以很好地加载。
我希望它的工作方式是,如果调用getQuestions(),则返回的对象将没有答案(因为延迟加载的对象不会在任何地方调用)。然而,这只是给了我一个错误。如果我使用连接获取进行查询,它也会显示答案(预期行为)。
我做错了什么?我在不同的地方尝试了@Transactional,但没有成功。我也没有。xml文件—到目前为止,所有操作都是使用注释完成的。
我得到的错误是:
exception
org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: failed to lazily initialize a collection of role: com.testApp.domain.InitiativeProfileQuestion.answers, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.testApp.domain.InitiativeProfileQuestion["answers"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.testApp.domain.InitiativeProfileQuestion.answers, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.testApp.domain.InitiativeProfileQuestion["answers"])
org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:238)
org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:208)
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:161)
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:101)
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:185)
org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:71)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:126)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:858)
javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
root cause
com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.testApp.domain.InitiativeProfileQuestion.answers, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.testApp.domain.InitiativeProfileQuestion["answers"])
com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:210)
com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:177)
com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:187)
com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:647)
com.fasterxml.jackson.databind.ser.std.BeanSerializerBase._serializeWithObjectId(BeanSerializerBase.java:558)
com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:145)
com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100)
com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:21)
com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:183)
com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:128)
com.fasterxml.jackson.databind.ObjectMapper.writeValue(ObjectMapper.java:1902)
org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:231)
org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:208)
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:161)
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:101)
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:185)
org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:71)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:126)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:858)
javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
正如您从stacktrac中看到的,错误发生在Jackson试图访问延迟加载的对象以便将其序列化为JSON时。此时,Spring事务已经完成,Hibernate会话关闭,这就是为什么Hibernate不能再加载该对象。
如果不打算序列化该字段,则可能希望使用@JsonIgnore或Spring的Jackson序列化视图支持。
对于延迟加载情况下的异常,您必须尝试在会话外部获取关联对象。将延迟加载更改为“渴望”,或者将获取关联对象的代码放在会话中。例如:
public void test() {
Session session = HibernateUtil.currentSession();
session.beginTransaction();
Vehicle vehicle= (Vehicle) session.get(Vehicle.class, 2);
System.out.println(vehicle.getVehicleName());
session.getTransaction().commit();
session.close();
System.out.println(vehicle.getVehicleName()); //No exception here
System.out.println(vehicle.getUser().getUserName());
// Exception here change the loading to EAGER or put this line of code within the session above. Put it before session.close() or before session.getTransaction().commit();
}
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