refactor: 지출 내역 추가 로직 수정

server/src/main/java/server/haengdong/application/BillActionService.java

@@ -1,6 +1,5 @@
 package server.haengdong.application;
 
-import java.util.ArrayList;
 import java.util.List;
 import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
@@ -26,20 +25,18 @@ public class BillActionService {
     public void saveAllBillAction(String eventToken, List<BillActionAppRequest> requests) {
         Event event = eventRepository.findByToken(eventToken)
                 .orElseThrow(() -> new IllegalArgumentException("존재하지 않는 이벤트 토큰입니다."));
-        long lastSequence = getLastSequence(event);
+        Action action = createStartAction(event);
 
-        List<BillAction> billActions = new ArrayList<>();
         for (BillActionAppRequest request : requests) {
-            Action action = new Action(event, ++lastSequence);
             BillAction billAction = request.toBillAction(action);
-            billActions.add(billAction);
+            billActionRepository.save(billAction);
+            action = action.next();
         }
-        billActionRepository.saveAll(billActions);
     }
 
-    private long getLastSequence(Event event) {
+    private Action createStartAction(Event event) {
         return actionRepository.findLastByEvent(event)
-                .map(Action::getSequence)
-                .orElse(0L);
+                .map(Action::next)
+                .orElse(Action.createFirst(event));
     }
 }

server/src/main/java/server/haengdong/domain/Action.java

@@ -15,6 +15,8 @@
 @Entity
 public class Action {
 
+    private static final long FIRST_SEQUENCE = 1L;
+
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private Long id;
@@ -28,4 +30,12 @@ public Action(Event event, Long sequence) {
         this.event = event;
         this.sequence = sequence;
     }
+
+    public static Action createFirst(Event event) {
+        return new Action(event, FIRST_SEQUENCE);
+    }
+
+    public Action next() {
+        return new Action(event, sequence + 1);
+    }
 }

server/src/test/java/server/haengdong/domain/ActionTest.java

@@ -0,0 +1,29 @@
+package server.haengdong.domain;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+class ActionTest {
+
+    @DisplayName("액션의 초기 순서번호는 1이다.")
+    @Test
+    void createFirst() {
+        Event event = new Event("name", "token");
+        Action action = Action.createFirst(event);
+
+        assertThat(action.getSequence()).isOne();
+    }
+
+    @DisplayName("현재 액션의 다음 액션의 순서는 1만큼 증가한다.")
+    @Test
+    void next() {
+        Event event = new Event("name", "token");
+        Action action = new Action(event, 2L);
+
+        Action nextAction = action.next();
+
+        assertThat(nextAction.getSequence()).isEqualTo(3L);
+    }
+}