@JsonIgnore 사용과 지연로딩 에러

개발일지/JPA

@JsonIgnore 사용과 지연로딩 에러

티에리앙리 2022. 8. 1. 20:11

JPA 사용 시 양방향 관계를 조회하면

양방향 참조로 인한 무한 루프가 발생할 수 있다.

ex) 다음 API를 호출하면

@GetMapping("/api/v1/simple-orders")
public List<Order> ordersV1() {
    List<Order> all = orderRepository.findAllByString(new OrderSearch());
    return all;
}

이렇게 Order 의 List를 조회하게 되면

Order 클래스에 있는 Member를 조회하게 되는데

public class Order {

    @Id @GeneratedValue
    @Column(name = "order_id")
    private Long id;

    @ManyToOne(fetch = LAZY)    // 지연로딩이면 진짜 Member 객체를 안끌고 온다. 즉, Member를 상속받아서 proxy Member 객체를 생성해서 넣어둔다.
    @JoinColumn(name = "memder_id")
    private Member member;
    
    // ...

Member 클래스에도 Order가 있게 되어 무한 참조가 일어난다.

public class Member {

    @Id @GeneratedValue
    @Column(name = "member_id")
    private Long id;

    @OneToMany(mappedBy = "member")
    private List<Order> orders = new ArrayList<>();
    
    // ...
}

그러므로 이럴 땐 무한참조가 일어나지 않게 하기 위해서

@JsonIgnore 어노테이션을 한쪽에 추가 해야한다.

public class Member {

    @Id @GeneratedValue
    @Column(name = "member_id")
    private Long id;

    @JsonIgnore // 양 방향 연관관계에서는 명시해야한다. 안그러면 무한 루프로 참조한다
    @OneToMany(mappedBy = "member")
    private List<Order> orders = new ArrayList<>();

	// ...
}

그러면 무한 참조는 일어나지 않지만 api를 요청하면 또 다른 에러가 발생한다.

간단한 테스트이므로 테스트 코드 작성 전 포스트맨으로 돌려봤는데 다음과 같은 에러가 발생한다.

아래와 같은 에러가 발생하는 이유는 엔티티를 반환했기 때문이다. dto를 반환했으면 에러는 발생하지 않느다.

{ "timestamp": "2022-08-01T10:59:18.716+00:00", "status": 500, "error": "Internal Server Error", "trace": "org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0]->jpabook.jpashop.domain.Order[\"member\"]->jpabook.jpashop.domain.Member$HibernateProxy$fQq9BNA1[\"hibernateLazyInitializer\"])\r\n\tat org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:462)\r\n\tat org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:104)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:290)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:183)\r\n\tat org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:78)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:135)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)\r\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\r\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067)\r\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)\r\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)\r\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)\r\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:655)\r\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)\r\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:764)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\r\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\r\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\r\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)\r\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)\r\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)\r\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)\r\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)\r\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)\r\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)\r\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)\r\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)\r\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890)\r\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1787)\r\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)\r\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)\r\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)\r\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)\r\n\tat java.lang.Thread.run(Thread.java:750)\r\nCaused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0]->jpabook.jpashop.domain.Order[\"member\"]->jpabook.jpashop.domain.Member$HibernateProxy$fQq9BNA1[\"hibernateLazyInitializer\"])\r\n\tat com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77)\r\n\tat com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1300)\r\n\tat com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:400)\r\n\tat com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:46)\r\n\tat com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:29)\r\n\tat com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:728)\r\n\tat com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774)\r\n\tat com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178)\r\n\tat com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:728)\r\n\tat com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:774)\r\n\tat com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:178)\r\n\tat com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:145)\r\n\tat com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:107)\r\n\tat com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:25)\r\n\tat com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)\r\n\tat com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:400)\r\n\tat com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1514)\r\n\tat com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:1007)\r\n\tat org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:456)\r\n\t... 48 more\r\n", "message": "Type definition error: [simple type, class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.ArrayList[0]->jpabook.jpashop.domain.Order[\"member\"]->jpabook.jpashop.domain.Member$HibernateProxy$fQq9BNA1[\"hibernateLazyInitializer\"])", "path": "/api/v1/simple-orders" }

정말 간단한 애플리케이션이 아니면 엔티티를 API 응답으로 외부로 노출하는 것은 좋지 않다. 따라서 Hibernate5Module 를 사용하기 보다는 DTO로 변환해서 반환하는 것이 더 좋은 방법이다.

결론은 dto로 반환하면 된다.