[refactor#148] 답변 채택 API 성능 최적화

src/main/java/com/dnd/gongmuin/answer/controller/AnswerController.java

@@ -52,10 +52,21 @@ public ResponseEntity<PageResponse<AnswerDetailResponse>> getAnswersByQuestionPo
 	@ApiResponse(useReturnTypeSchema = true)
 	@PostMapping("/api/question-posts/answers/{answerId}")
 	public ResponseEntity<AnswerDetailResponse> getAnswersByQuestionPostId(
-		@PathVariable Long answerId,
+		@PathVariable("answerId") Long answerId,
 		@AuthenticationPrincipal Member member
 	) {
 		AnswerDetailResponse response = answerService.chooseAnswer(answerId, member);
 		return ResponseEntity.ok(response);
 	}
+
+	@Operation(summary = "답변 채택 API", description = "질문자가 답변을 채택한다.")
+	@ApiResponse(useReturnTypeSchema = true)
+	@PostMapping("/api/v2/question-posts/answers/{answerId}")
+	public ResponseEntity<AnswerDetailResponse> getAnswersByQuestionPostIdV2(
+		@PathVariable("answerId") Long answerId,
+		@AuthenticationPrincipal Member member
+	) {
+		AnswerDetailResponse response = answerService.chooseAnswerV2(answerId, member);
+		return ResponseEntity.ok(response);
+	}
 }

src/main/java/com/dnd/gongmuin/answer/repository/AnswerSimpleQueryRepository.java

@@ -0,0 +1,28 @@
+package com.dnd.gongmuin.answer.repository;
+
+import java.util.Optional;
+
+import org.springframework.stereotype.Repository;
+
+import com.dnd.gongmuin.answer.domain.Answer;
+
+import jakarta.persistence.EntityManager;
+import lombok.RequiredArgsConstructor;
+
+@Repository
+@RequiredArgsConstructor
+public class AnswerSimpleQueryRepository {
+
+	private final EntityManager em;
+
+	public Optional<Answer> findAnswerById(Long answerId) {
+		Answer answer = em.createQuery(
+				"select a from Answer a" +
+					" join fetch a.member m" +
+					" where a.id = :answerId", Answer.class
+			)
+			.setParameter("answerId", answerId)
+			.getSingleResult();
+		return Optional.of(answer);
+	}
+}

src/main/java/com/dnd/gongmuin/answer/service/AnswerService.java

@@ -13,6 +13,7 @@
 import com.dnd.gongmuin.answer.dto.RegisterAnswerRequest;
 import com.dnd.gongmuin.answer.exception.AnswerErrorCode;
 import com.dnd.gongmuin.answer.repository.AnswerRepository;
+import com.dnd.gongmuin.answer.repository.AnswerSimpleQueryRepository;
 import com.dnd.gongmuin.common.dto.PageMapper;
 import com.dnd.gongmuin.common.dto.PageResponse;
 import com.dnd.gongmuin.common.exception.runtime.NotFoundException;
@@ -23,6 +24,7 @@
 import com.dnd.gongmuin.question_post.domain.QuestionPost;
 import com.dnd.gongmuin.question_post.exception.QuestionPostErrorCode;
 import com.dnd.gongmuin.question_post.repository.QuestionPostRepository;
+import com.dnd.gongmuin.question_post.repository.QuestionPostSimpleQueryRepository;
 
 import lombok.RequiredArgsConstructor;
 
@@ -34,6 +36,8 @@ public class AnswerService {
 	private final AnswerRepository answerRepository;
 	private final CreditHistoryService creditHistoryService;
 	private final ApplicationEventPublisher eventPublisher;
+	private final QuestionPostSimpleQueryRepository questionPostSimpleQueryRepository;
+	private final AnswerSimpleQueryRepository answerSimpleQueryRepository;
 
 	private static void validateIfQuestioner(Member member, QuestionPost questionPost) {
 		if (!questionPost.isQuestioner(member.getId())) {
@@ -85,6 +89,23 @@ public AnswerDetailResponse chooseAnswer(
 		return AnswerMapper.toAnswerDetailResponse(answer);
 	}
 
+	@Transactional
+	public AnswerDetailResponse chooseAnswerV2(
+		Long answerId,
+		Member member
+	) {
+		Answer answer = getAnswerByIdV2(answerId);
+		QuestionPost questionPost = findQuestionPostByIdV2(answer.getQuestionPostId());
+		validateIfQuestioner(member, questionPost);
+		chooseAnswer(questionPost, answer);
+
+		eventPublisher.publishEvent(new NotificationEvent(
+			CHOSEN, questionPost.getId(), member.getId(), answer.getMember()
+		));
+
+		return AnswerMapper.toAnswerDetailResponse(answer);
+	}
+
 	private void chooseAnswer(QuestionPost questionPost, Answer answer) {
 		questionPost.updateIsChosen(answer);
 		answer.getMember().increaseCredit(questionPost.getReward());
@@ -108,4 +129,14 @@ private QuestionPost findQuestionPostById(Long questionPostId) {
 		return questionPostRepository.findById(questionPostId)
 			.orElseThrow(() -> new NotFoundException(QuestionPostErrorCode.NOT_FOUND_QUESTION_POST));
 	}
+
+	private Answer getAnswerByIdV2(Long answerId) {
+		return answerSimpleQueryRepository.findAnswerById(answerId)
+			.orElseThrow(() -> new NotFoundException(AnswerErrorCode.NOT_FOUND_ANSWER));
+	}
+
+	private QuestionPost findQuestionPostByIdV2(Long questionPostId) {
+		return questionPostSimpleQueryRepository.findQuestionPostById(questionPostId)
+			.orElseThrow(() -> new NotFoundException(QuestionPostErrorCode.NOT_FOUND_QUESTION_POST));
+	}
 }

src/main/java/com/dnd/gongmuin/question_post/repository/QuestionPostSimpleQueryRepository.java

@@ -0,0 +1,28 @@
+package com.dnd.gongmuin.question_post.repository;
+
+import java.util.Optional;
+
+import org.springframework.stereotype.Repository;
+
+import com.dnd.gongmuin.question_post.domain.QuestionPost;
+
+import jakarta.persistence.EntityManager;
+import lombok.RequiredArgsConstructor;
+
+@Repository
+@RequiredArgsConstructor
+public class QuestionPostSimpleQueryRepository {
+
+	private final EntityManager em;
+
+	public Optional<QuestionPost> findQuestionPostById(Long questionPostId) {
+		QuestionPost questionPost = em.createQuery(
+				"select q from QuestionPost q" +
+					" join fetch q.member m" +
+					" where q.id = :questionPostId", QuestionPost.class
+			)
+			.setParameter("questionPostId", questionPostId)
+			.getSingleResult();
+		return Optional.of(questionPost);
+	}
+}

src/test/java/com/dnd/gongmuin/answer/controller/AnswerControllerTest.java

@@ -125,6 +125,7 @@ void chooseAnswer() throws Exception {
 			= questionPostRepository.save(QuestionPostFixture.questionPost(loginMember));
 		Member answerer = memberRepository.save(MemberFixture.member2());
 		Answer answer = answerRepository.save(AnswerFixture.answer(questionPost.getId(), answerer));
+		long startTime = System.currentTimeMillis();
 
 		mockMvc.perform(post("/api/question-posts/answers/{answerId}", answer.getId())
 				.cookie(accessToken)
@@ -137,5 +138,31 @@ void chooseAnswer() throws Exception {
 			.andExpect(jsonPath("$.memberInfo.nickname").value(answerer.getNickname()))
 			.andExpect(jsonPath("$.memberInfo.memberJobGroup").value(answerer.getJobGroup().getLabel())
 			);
+		long endTime = System.currentTimeMillis();
+		System.out.println("Execution time: " + (endTime - startTime) + " ms");
+	}
+
+	@DisplayName("[질문자는 답변을 채택할 수 있다.V2]")
+	@Test
+	void chooseAnswerV2() throws Exception {
+		QuestionPost questionPost
+			= questionPostRepository.save(QuestionPostFixture.questionPost(loginMember));
+		Member answerer = memberRepository.save(MemberFixture.member2());
+		Answer answer = answerRepository.save(AnswerFixture.answer(questionPost.getId(), answerer));
+		long startTime = System.currentTimeMillis();
+
+		mockMvc.perform(post("/api/v2/question-posts/answers/{answerId}", answer.getId())
+				.cookie(accessToken)
+			)
+			.andExpect(status().isOk())
+			.andExpect(jsonPath("$.content").value(answer.getContent()))
+			.andExpect(jsonPath("$.isChosen").value(true))
+			.andExpect(jsonPath("$.isQuestioner").value(false))
+			.andExpect(jsonPath("$.memberInfo.memberId").value(answerer.getId()))
+			.andExpect(jsonPath("$.memberInfo.nickname").value(answerer.getNickname()))
+			.andExpect(jsonPath("$.memberInfo.memberJobGroup").value(answerer.getJobGroup().getLabel())
+			);
+		long endTime = System.currentTimeMillis();
+		System.out.println("Execution time: " + (endTime - startTime) + " ms");
 	}
 }

src/test/java/com/dnd/gongmuin/answer/service/AnswerServiceTest.java

@@ -4,8 +4,12 @@
 import static org.junit.jupiter.api.Assertions.*;
 import static org.mockito.BDDMockito.*;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 
 import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.DisplayName;
@@ -24,6 +28,7 @@
 import com.dnd.gongmuin.answer.dto.AnswerDetailResponse;
 import com.dnd.gongmuin.answer.dto.RegisterAnswerRequest;
 import com.dnd.gongmuin.answer.repository.AnswerRepository;
+import com.dnd.gongmuin.answer.repository.AnswerSimpleQueryRepository;
 import com.dnd.gongmuin.common.dto.PageResponse;
 import com.dnd.gongmuin.common.exception.runtime.ValidationException;
 import com.dnd.gongmuin.common.fixture.AnswerFixture;
@@ -36,6 +41,7 @@
 import com.dnd.gongmuin.question_post.domain.QuestionPost;
 import com.dnd.gongmuin.question_post.exception.QuestionPostErrorCode;
 import com.dnd.gongmuin.question_post.repository.QuestionPostRepository;
+import com.dnd.gongmuin.question_post.repository.QuestionPostSimpleQueryRepository;
 
 @DisplayName("[AnswerService 테스트]")
 @ExtendWith(MockitoExtension.class)
@@ -46,9 +52,15 @@ class AnswerServiceTest {
 	@Mock
 	private QuestionPostRepository questionPostRepository;
 
+	@Mock
+	private QuestionPostSimpleQueryRepository questionPostSimpleQueryRepository;
+
 	@Mock
 	private AnswerRepository answerRepository;
 
+	@Mock
+	private AnswerSimpleQueryRepository answerSimpleQueryRepository;
+
 	@Mock
 	private CreditHistoryService creditHistoryService;
 
@@ -130,6 +142,27 @@ void chooseAnswer() {
 		Assertions.assertThat(response.isChosen()).isTrue();
 	}
 
+	@DisplayName("[답변을 채택할 수 있다.]")
+	@Test
+	void chooseAnswerV2() {
+		//given
+		Long questionPostId = 1L;
+		Member member = MemberFixture.member(1L);
+		QuestionPost questionPost = QuestionPostFixture.questionPost(questionPostId, member);
+		Answer answer = AnswerFixture.answer(1L, questionPostId);
+
+		given(answerSimpleQueryRepository.findAnswerById(answer.getId()))
+			.willReturn(Optional.of(answer));
+		given(questionPostSimpleQueryRepository.findQuestionPostById(questionPost.getId()))
+			.willReturn(Optional.of(questionPost));
+
+		//when
+		AnswerDetailResponse response = answerService.chooseAnswerV2(answer.getId(), member);
+
+		//then
+		Assertions.assertThat(response.isChosen()).isTrue();
+	}
+
 	@DisplayName("[크레딧이 부족하면 답변을 채택할 수 없다.]")
 	@Test
 	void chooseAnswer_fail() {
@@ -172,4 +205,54 @@ void chooseAnswer_fail2() {
 			.isInstanceOf(ValidationException.class)
 			.hasMessageContaining(QuestionPostErrorCode.NOT_AUTHORIZED.getMessage());
 	}
+
+	@DisplayName("[동시에 10_000개의 채택이 일어나 크레딧을 입금 받는다.]")
+	@Test
+	void creditHistoryWithOneHundred() throws Exception {
+		// given
+		final long threadCount = 10_000L;
+		final int writerCredit = 10_000_000;
+		ExecutorService executorService = Executors.newFixedThreadPool(32);
+		CountDownLatch latch = new CountDownLatch((int)threadCount);
+
+		Member writer = MemberFixture.member(1L);
+		Member answer = MemberFixture.member(2L);
+		ReflectionTestUtils.setField(writer, "credit", writerCredit);
+		ReflectionTestUtils.setField(answer, "credit", 0);
+
+		List<QuestionPost> questionPosts = new ArrayList<>();
+		List<Answer> answers = new ArrayList<>();
+
+		for (long i = 1L; i <= threadCount; i++) {
+			QuestionPost questionPost = QuestionPostFixture.questionPost(i, writer);
+
+			Answer answer1 = AnswerFixture.answer(questionPost.getId(), answer);
+			ReflectionTestUtils.setField(answer1, "id", i);
+			questionPosts.add(questionPost);
+			answers.add(answer1);
+
+			given(answerRepository.findById(i)).willReturn(Optional.of(answer1));
+			given(questionPostRepository.findById(questionPost.getId())).willReturn(Optional.of(questionPost));
+		}
+
+		// when
+		long startTime = System.currentTimeMillis();
+		for (long i = 0L; i < threadCount; i++) {
+			final int index = (int)i;
+			executorService.submit(() -> {
+				try {
+					answerService.chooseAnswer(answers.get(index).getId(), writer);
+				} finally {
+					latch.countDown();
+				}
+			});
+		}
+		latch.await();
+
+		long endTime = System.currentTimeMillis();
+		System.out.println("Execution time: " + (endTime - startTime) + " ms");
+
+		// then
+		assertEquals(answer.getCredit(), writerCredit);
+	}
 }