♻️ refactor: userId 기반 단건 조회 쿼리 메서드로 성능 개선

Author: jiwon1217

backend/src/main/java/io/f1/backend/domain/stat/dao/StatJpaRepository.java

@@ -63,4 +63,14 @@ public interface StatJpaRepository extends JpaRepository<Stat, Long> {
             		s.user.id = :userId
             """)
     void updateStatByUserIdCaseLose(long deltaScore, long userId);
+
+    @Query(
+            """
+            SELECT new io.f1.backend.domain.stat.dto.StatWithNicknameAndUserId(
+                u.id, u.nickname, s.totalGames, s.winningGames, s.score
+            )
+            FROM Stat s JOIN s.user u
+            WHERE u.id = :userId
+            """)
+    Optional<StatWithNicknameAndUserId> findByUserId(long userId);
 }

backend/src/main/java/io/f1/backend/domain/stat/dao/StatRepositoryAdapter.java

@@ -108,17 +108,15 @@ public MyPageInfo getMyPageByUserId(long userId) {
             log.error("Redis miss, fallback to MySQL for userId={}", userId, e);
         }
 
-        StatWithNicknameAndUserId stat = findFirstMatchingStat(userId);
+        StatWithNicknameAndUserId stat = findStatByUserId(userId);
         long rank = jpaRepository.countByScoreGreaterThan(stat.score()) + 1;
 
         return new MyPageInfo(
                 stat.nickname(), rank, stat.totalGames(), stat.winningGames(), stat.score());
     }
 
-    private StatWithNicknameAndUserId findFirstMatchingStat(long userId) {
-        return jpaRepository.findAllStatWithNicknameAndUserId().stream()
-                .filter(stat -> stat.userId() == userId)
-                .findFirst()
-                .orElseThrow(() -> new CustomException(UserErrorCode.USER_NOT_FOUND));
+    private StatWithNicknameAndUserId findStatByUserId(long userId) {
+        return jpaRepository.findByUserId(userId)
+            .orElseThrow(() -> new CustomException(UserErrorCode.USER_NOT_FOUND));
     }
 }