[Fix] Quiz 엔티티 영속성 컨텍스트 꼬임 문제 해결

src/main/java/com/_1/spring_rest_api/entity/CustomQuiz.java

@@ -90,8 +90,14 @@ public void addQuestion(Question question) {
             return; // 이미 추가된 질문이면 무시
         }
 
-        // 정적 팩토리 메서드를 통해 매핑 생성 및 양방향 연관관계 설정
-        QuizQuestionMapping.create(this, question);
+        // 매핑 생성 및 양방향 연관관계 설정
+        QuizQuestionMapping mapping = QuizQuestionMapping.builder()
+                .quiz(this)
+                .question(question)
+                .build();
+
+        this.quizQuestionMappings.add(mapping);
+        question.getQuizQuestionMappings().add(mapping);
 
         // 질문 수 증가
         this.updateTotalQuestions(this.totalQuestions + 1);

src/main/java/com/_1/spring_rest_api/entity/QuizQuestionMapping.java

@@ -27,11 +27,4 @@ public class QuizQuestionMapping extends BaseTimeEntity {
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "question_id")
     private Question question;
-
-    public static QuizQuestionMapping create(CustomQuiz quiz, Question question) {
-        return QuizQuestionMapping.builder()
-                .quiz(quiz)
-                .question(question)
-                .build();
-    }
 }

src/main/java/com/_1/spring_rest_api/service/QuizCommandServiceImpl.java

@@ -9,6 +9,7 @@
 import org.springframework.transaction.annotation.Transactional;
 
 import java.util.*;
+import java.util.stream.Collectors;
 
 @Service
 @Transactional
@@ -42,7 +43,7 @@ public Long createQuiz(CreateQuizRequest request) {
         connectWeeksToQuiz(request.getWeekIds(), savedQuiz);
 
         // 질문 처리
-        processQuestions(request, savedQuiz);
+        processQuestionsWithFreshEntities(request, savedQuiz);
 
         return savedQuiz.getId();
     }
@@ -98,43 +99,33 @@ private void connectWeeksToQuiz(List<Long> weekIds, CustomQuiz quiz) {
     }
 
     // 질문 처리 로직
-    private void processQuestions(CreateQuizRequest request, CustomQuiz quiz) {
-        Set<Question> questions = new HashSet<>();
-
-        // 주차 기반 질문 선택
-        if (request.getWeekIds() != null && !request.getWeekIds().isEmpty()) {
-            // 선택된 모든 주차의 질문 가져오기
-            List<Question> weekQuestions = getQuestionList(request);
-
-            // 질문 수 제한이 있는 경우 랜덤 선택
-            weekQuestions = getRandomQuestionsIfHasLimit(request, weekQuestions);
-
-            questions.addAll(weekQuestions);
+    private void processQuestionsWithFreshEntities(CreateQuizRequest request, CustomQuiz quiz) {
+        if (request.getWeekIds() == null || request.getWeekIds().isEmpty()) {
+            return;
         }
 
-        // 질문 중복 제거 및 퀴즈에 추가
-        for (Question question : questions) {
-            quiz.addQuestion(question);
+        // 👇 week별로 질문 ID만 수집
+        List<Long> questionIds = new ArrayList<>();
+        for (Long weekId : request.getWeekIds()) {
+            List<Long> weekQuestionIds = questionRepository.findAllByWeekId(weekId)
+                    .stream()
+                    .map(Question::getId)
+                    .toList();
+            questionIds.addAll(weekQuestionIds);
         }
 
-        customQuizRepository.save(quiz);
-    }
-
-    private static List<Question> getRandomQuestionsIfHasLimit(CreateQuizRequest request, List<Question> weekQuestions) {
+        // 랜덤 선택
         if (request.getQuestionCount() != null && request.getQuestionCount() > 0 &&
-                request.getQuestionCount() < weekQuestions.size()) {
-            // 무작위 선택
-            Collections.shuffle(weekQuestions);
-            weekQuestions = weekQuestions.subList(0, request.getQuestionCount());
+                request.getQuestionCount() < questionIds.size()) {
+            Collections.shuffle(questionIds);
+            questionIds = questionIds.subList(0, request.getQuestionCount());
         }
-        return weekQuestions;
-    }
 
-    private List<Question> getQuestionList(CreateQuizRequest request) {
-        List<Question> weekQuestions = new ArrayList<>();
-        for (Long weekId : request.getWeekIds()) {
-            weekQuestions.addAll(questionRepository.findAllByWeekId(weekId));
+        List<Question> freshQuestions = questionRepository.findAllById(questionIds);
+
+        for (Question question : freshQuestions) {
+            quiz.addQuestion(question);
         }
-        return weekQuestions;
     }
+
 }