Update README.md

so2zy · Dec 15, 2023 · 22a314d · 22a314d
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 ## ✅ ERD
 ![ERD](https://github.com/so2zy/so2zy_BE/assets/139187207/3c2bdb39-d128-4568-a0f7-f61d746e6897)
 
+
 ## 💯 에러 해결 방안
+<details>
+<summary>에러 내용 및 해결</summary>
+
+### 1. StackOverFlow Error 문제
+
+**1 - 1. 원인**
+
+```bash
+Infinite recursion (StackOverflowError) 
+(through reference chain: com.aroom.domain.room.model.Room["accommodation"]
+->com.aroom.domain.accommodation.model.Accommodation["roomList"]
+->org.hibernate.collection.spi.PersistentBag[0]
+->com.aroom.domain.room.model.Room["accommodation"]
+->com.aroom.domain.accommodation.model.Accommodation["roomList"]-
+```
+
+현재 양방향 연관관계에 놓여진 Accommodation과 Room에서 무한순환참조가 발생했다.
+<br>
+**1 - 2. 해결**
+
+- `@OneToMany` `@manytoone`로 인해 순환참조 원인
+- `@JsonManagedReference` & `@JsonBackReference` 추가
+
+```java
+@JsonManagedReference
+@OneToMany(mappedBy = "accommodation", fetch = FetchType.LAZY)
+private List<Room> roomList = new ArrayList<>();
+```
+
+- `@JsonManagedReference` : 부모 `Entity` → 자식 `Entity`
+    - 정상적으로 직렬화를 수행
+
+```java
+@JsonBackReference
+@ManyToOne(fetch = FetchType.LAZY)
+@JoinColumn(name = "accommodation_id")
+private Accommodation accommodation;
+```
+
+- `@JsonBackReference` : 자식`Entity` → 부모 `Entity`
+    - 직렬화 수행 x
+        
+        ⇒ 무한 순환 참조 해결
+        
+<br>
+
+### 2. Jackson 직렬화 제한자 문제
+
+**2 - 1. 발생 과정**
+
+```java
+public RoomCartResponseDTO postRoomCart(Long member_id, Long room_id){
+    Room room = roomRepository.findById(room_id).get();
+    Cart cart = cartRepository.findByMemberId(member_id).get();
+    RoomCart roomCart = roomCartRepository.save(new RoomCart(cart,room));
+    cart.postRoomCarts(roomCart);
+    return new RoomCartResponseDTO(cart);
+}
+```
+
+```java
+@OneToMany(mappedBy = "cart", fetch = FetchType.LAZY)
+private List<RoomCart> roomCartList = new ArrayList<>();
+
+public void postRoomCarts(RoomCart roomCart){
+	roomCartList.add(roomCart);
+}
+```
+
+객실을 장바구니에 담을 때 RoomCart를 생성하여 Cart의 List<RoomCart> roomCartList에 post 시도
+<br>
+
+**2 - 2. 원인**
+
+```bash
+Type definition error: [simple type, class com.aroom.domain.roomCart.dto.response.RoomCartResponseDTO]
+```
+
+```bash
+org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class com.aroom.domain.roomCart.dto.response.RoomCartResponseDTO]
+at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:489) ~[spring-web-6.0.13.jar:6.0.13]
+at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:103) ~[spring-web-6.0.13.jar:6.0.13]
+at
+```
+
+```bash
+caused by: com.fasterxml.jackson.databind.exc.invaliddefinitionexception: 
+no serializer found for class com.aroom.domain.roomcart.dto.response.roomcartresponsedto 
+and no properties discovered to create beanserializer 
+(to avoid exception, disable serializationfeature.fail_on_empty_beans) 
+(through reference chain: com.aroom.global.response.apiresponse["data"])
+```
+
+- Jackson 라이브러리가 `RoomCartResponseDTO` & `RoomCartInfoDTO`를 직렬화할 때 문제가 발생
+- Jackson은 기본적으로 클래스를 직렬화할 때 해당 클래스에 대한 직렬화 메소드를 찾아야 하는데, 여기서는 해당 메소드를 찾지 못했다고 나온다.
+- 또한, Jackson은 직렬화 하는 과정에서 기본으로 접근 제한자가 public이거나, getter/setter를 이용하기 때문에 인스턴스 필드를 private등으로 선언시, json으로 변환 과정에서 에러가 발생한다.
+<br>
+
+**2 - 3. 해결**
+
+```java
+@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
+public class RoomCartResponseDTO {
+
+    private long cart_id;
+    private List<RoomCartInfoDTO> roomCartList;
+
+    public RoomCartResponseDTO(Cart cart) {
+        this.cart_id = cart.getId();
+        List<RoomCartInfoDTO> roomCartInfoDTOList = new ArrayList<>();
+        for(RoomCart roomCart : cart.getRoomCartList()){
+            RoomCartInfoDTO roomCartInfoDTO = new RoomCartInfoDTO(roomCart);
+            roomCartInfoDTOList.add(roomCartInfoDTO);
+        }
+        System.out.println(roomCartInfoDTOList.size()); // 정확히 나옴
+        this.roomCartList = roomCartInfoDTOList;
+    }
+}
+```
+
+```java
+@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
+public class RoomCartInfoDTO {
+
+    private long room_id;
+    private long cart_id;
+
+    @Builder
+    public RoomCartInfoDTO(long room_id, long cart_id) {
+        this.room_id = room_id;
+        this.cart_id = cart_id;
+    }
+
+    public RoomCartInfoDTO(RoomCart roomCart) {
+        this.room_id = roomCart.getRoom().getId();
+        this.cart_id = roomCart.getCart().getId();
+    }
+}
+```
+
+- JsonAutoDetect 설정 제거
+    
+    `@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)`
+    
+    - private 필드에 접근 가능하여 json으로 변환 가능하다.
+- Fetch.Type을 EAGER로 바꾸는 것은 보안의 문제가 있으므로 고려하지 않았습니다.
+- 또한, Entity Class에 @JsonProperty 또는 @JsonAutoDetect를 직접 선언할 수 있으나, Entity를 최대한 변경하지 않고자 DTO에 선언했습니다.
+<br>
+
+### 3. JPAQueryFactory 전역 설정과 DataJpaTest
+
+**3 - 1. 원인**
+
+```java
+Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.querydsl.jpa.impl.JPAQueryFactory' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
+	at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1824)
+	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1383)
+	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1337)
+	at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:910)
+	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:788)
+	... 108 more
+```
+
+해당 설정은 전역적으로 빈을 컨테이너에 생성하는 것이기 때문에 `Entity`와 `Respository` 빈만 생성하는 `@DataJpaTest의` 경우에는 `JpaQueryFactory` 빈을 생성하지 못하는 문제가 생기게 됩니다.
+<br>
+
+**3 - 2. 해결**
+
+```java
+@Configuration
+@EnableJpaAuditing
+@EnableJpaRepositories(basePackages = "com.aroom")
+public class JpaConfig {
+
+    @PersistenceContext
+    private EntityManager entityManager;
+
+    @Bean
+    public JPAQueryFactory queryFactory() {
+        return new JPAQueryFactory(entityManager);
+    }
+
+}
+```
+
+해당 문제를 해결하기 위해서는 실제 `JPAQueryFactory`를 사용하는 곳에서만 해당 빈을 생성하면 됩니다.
+</details>
 
 ## 🤖 개인 역량 회고