Refactor: 팀 결정사항 목록 조회 N+1 개선

src/main/java/com/whylog/server/domain/decision/dto/DecisionResponse.java

@@ -9,6 +9,14 @@
 
 public class DecisionResponse {
 
+    public record DecisionFlatRow(
+            Long decisionId,
+            String meetingName,
+            Long applicationId,
+            String applicationName
+    ) {
+    }
+
     @Getter
     @NoArgsConstructor
     @AllArgsConstructor

src/main/java/com/whylog/server/domain/team/repository/TeamRepository.java

@@ -1,6 +1,6 @@
 package com.whylog.server.domain.team.repository;
 
-import com.whylog.server.domain.decision.entity.Decision;
+import com.whylog.server.domain.decision.dto.DecisionResponse;
 import com.whylog.server.domain.team.entity.Team;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
@@ -13,12 +13,18 @@ public interface TeamRepository extends JpaRepository<Team, Long> {
     Boolean existsByName(String teamName);
 
     @Query("""
-      SELECT DISTINCT d
+      SELECT new com.whylog.server.domain.decision.dto.DecisionResponse$DecisionFlatRow(
+        d.id,
+        m.name,
+        a.id,
+        a.name
+      )
       FROM Decision d
-      JOIN FETCH d.meeting m
-      LEFT JOIN FETCH d.applications
+      JOIN d.meeting m
+      LEFT JOIN d.applications a
       WHERE m.team.id = :teamId
+      ORDER BY d.id
   """)
-    List<Decision> findDecisions(@Param("teamId") Long teamId);
+    List<DecisionResponse.DecisionFlatRow> findDecisionRows(@Param("teamId") Long teamId);
 
 }

src/main/java/com/whylog/server/domain/team/service/TeamQueryService.java

@@ -2,13 +2,15 @@
 
 import com.whylog.server.domain.decision.dto.ApplicationResponse;
 import com.whylog.server.domain.decision.dto.DecisionResponse;
-import com.whylog.server.domain.decision.entity.Decision;
 import com.whylog.server.domain.team.repository.TeamRepository;
 import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Map;
 
 @Service
 @RequiredArgsConstructor
@@ -19,22 +21,40 @@ public class TeamQueryService {
     @Transactional(readOnly = true)
     public List<DecisionResponse.DecisionListDTO> decisions( Long teamId ){
 
-        List<Decision> decisions = teamRepository.findDecisions(teamId);
-
-        return decisions.stream()
-                .map(d -> DecisionResponse.DecisionListDTO.builder()
-                        .decisionId(d.getId())
-                        .name(d.getMeeting().getName())
-                        .applications(
-                                d.getApplications().stream()
-                                        .map(application -> ApplicationResponse.ApplicationDTO.builder()
-                                                .applicationId(application.getId())
-                                                .name(application.getName())
-                                                .build())
-                                        .toList()
-                        )
-                        .build()
-                ).toList();
+        List<DecisionResponse.DecisionFlatRow> rows = teamRepository.findDecisionRows(teamId);
+        Map<Long, DecisionAccumulator> decisions = new LinkedHashMap<>();
+
+        for (DecisionResponse.DecisionFlatRow row : rows) {
+            DecisionAccumulator decision = decisions.computeIfAbsent(
+                    row.decisionId(),
+                    decisionId -> new DecisionAccumulator(decisionId, row.meetingName())
+            );
+
+            if (row.applicationId() != null) {
+                decision.applications().add(ApplicationResponse.ApplicationDTO.builder()
+                        .applicationId(row.applicationId())
+                        .name(row.applicationName())
+                        .build());
+            }
+        }
+
+        return decisions.values().stream()
+                .map(decision -> DecisionResponse.DecisionListDTO.builder()
+                        .decisionId(decision.decisionId())
+                        .name(decision.meetingName())
+                        .applications(decision.applications())
+                        .build())
+                .toList();
+    }
+
+    private record DecisionAccumulator(
+            Long decisionId,
+            String meetingName,
+            List<ApplicationResponse.ApplicationDTO> applications
+    ) {
+        private DecisionAccumulator(Long decisionId, String meetingName) {
+            this(decisionId, meetingName, new ArrayList<>());
+        }
     }
 
 }