Quiz exercises: Fix an error after using the practice mode

src/main/java/de/tum/cit/aet/artemis/quiz/repository/QuizSubmissionRepository.java

@@ -3,6 +3,7 @@
 import static de.tum.cit.aet.artemis.core.config.Constants.PROFILE_CORE;
 import static org.springframework.data.jpa.repository.EntityGraph.EntityGraphType.LOAD;
 
+import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 
@@ -37,7 +38,16 @@ public interface QuizSubmissionRepository extends ArtemisJpaRepository<QuizSubmi
     QuizSubmission findWithEagerSubmittedAnswersById(long submissionId);
 
     @EntityGraph(type = LOAD, attributePaths = { "submittedAnswers" })
-    Optional<QuizSubmission> findWithEagerSubmittedAnswersByParticipationId(long participationId);
+    List<QuizSubmission> findWithEagerSubmittedAnswersByParticipationId(long participationId);
+
+    @Query("""
+            SELECT submission
+            FROM QuizSubmission submission
+                LEFT JOIN FETCH submission.submittedAnswers
+                JOIN submission.results r
+            WHERE r.id = :resultId
+            """)
+    Optional<QuizSubmission> findWithEagerSubmittedAnswersByResultId(@Param("resultId") long resultId);
 
     /**
      * Retrieve QuizSubmission for given quiz batch and studentLogin

src/main/java/de/tum/cit/aet/artemis/quiz/service/QuizSubmissionService.java

@@ -147,7 +147,7 @@ public void calculateAllResults(long quizExerciseId) {
         log.info("Calculating results for quiz {}", quizExercise.getId());
         studentParticipationRepository.findByExerciseId(quizExercise.getId()).forEach(participation -> {
             participation.setExercise(quizExercise);
-            Optional<QuizSubmission> quizSubmissionOptional = quizSubmissionRepository.findWithEagerSubmittedAnswersByParticipationId(participation.getId());
+            Optional<QuizSubmission> quizSubmissionOptional = quizSubmissionRepository.findWithEagerSubmittedAnswersByParticipationId(participation.getId()).stream().findFirst();
 
             if (quizSubmissionOptional.isEmpty()) {
                 return;

src/main/java/de/tum/cit/aet/artemis/quiz/web/QuizParticipationResource.java

@@ -69,6 +69,8 @@ public QuizParticipationResource(QuizExerciseRepository quizExerciseRepository,
 
     /**
      * POST /quiz-exercises/{exerciseId}/start-participation : start the quiz exercise participation
+     * TODO: This endpoint is also called when viewing the result of a quiz exercise.
+     * TODO: This does not make any sense, as the participation is already started.
      *
      * @param exerciseId the id of the quiz exercise
      * @return The created participation
@@ -92,7 +94,14 @@ public ResponseEntity<MappingJacksonValue> startParticipation(@PathVariable Long
 
         // NOTE: starting exercise prevents that two participation will exist, but ensures that a submission is created
         var result = resultRepository.findFirstByParticipationIdAndRatedOrderByCompletionDateDesc(participation.getId(), true).orElse(new Result());
-        result.setSubmission(quizSubmissionRepository.findWithEagerSubmittedAnswersByParticipationId(participation.getId()).orElseThrow());
+        if (result.getId() == null) {
+            // Load the live submission of the participation
+            result.setSubmission(quizSubmissionRepository.findWithEagerSubmittedAnswersByParticipationId(participation.getId()).stream().findFirst().orElseThrow());
+        }
+        else {
+            // Load the actual submission of the result
+            result.setSubmission(quizSubmissionRepository.findWithEagerSubmittedAnswersByResultId(result.getId()).orElseThrow());
+        }
 
         participation.setResults(Set.of(result));
         participation.setExercise(exercise);