From 1f4fb139a308171c7acf6a05854e9273de4a5ca9 Mon Sep 17 00:00:00 2001
From: joyewon0705 <77885098+joyewon0705@users.noreply.github.com>
Date: Mon, 13 Oct 2025 15:41:51 +0900
Subject: [PATCH] =?UTF-8?q?Ref:=20Unique=20Key=20=EC=B6=A9=EB=8F=8C=20?=
 =?UTF-8?q?=EB=B0=8F=20flush=20=ED=83=80=EC=9D=B4=EB=B0=8D=20=EB=AC=B8?=
 =?UTF-8?q?=EC=A0=9C=20=ED=95=B4=EA=B2=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../back/domain/board/post/entity/Post.java   | 24 +++++++++++++++----
 .../board/post/service/PostService.java       |  7 +++---
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/main/java/com/back/domain/board/post/entity/Post.java b/src/main/java/com/back/domain/board/post/entity/Post.java
index 1365c631..863e21ce 100644
--- a/src/main/java/com/back/domain/board/post/entity/Post.java
+++ b/src/main/java/com/back/domain/board/post/entity/Post.java
@@ -62,6 +62,10 @@ public void addPostCategoryMapping(PostCategoryMapping mapping) {
         this.postCategoryMappings.add(mapping);
     }
 
+    public void removePostCategoryMapping(PostCategoryMapping mapping) {
+        this.postCategoryMappings.remove(mapping);
+    }
+
     public void addLike(PostLike like) {
         this.postLikes.add(like);
     }
@@ -93,11 +97,23 @@ public void update(String title, String content) {
         this.content = content;
     }
 
-    // TODO: 진짜로 바뀐 카테고리만 추가/삭제하도록 개선
     /** 카테고리 일괄 업데이트 */
-    public void updateCategories(List<PostCategory> categories) {
-        this.postCategoryMappings.clear();
-        categories.forEach(category -> new PostCategoryMapping(this, category));
+    public void updateCategories(List<PostCategory> newCategories) {
+        List<PostCategory> currentCategories = this.getCategories();
+
+        // 제거 대상
+        List<PostCategoryMapping> toRemove = this.getPostCategoryMappings().stream()
+                .filter(mapping -> !newCategories.contains(mapping.getCategory()))
+                .toList();
+
+        // 추가 대상
+        List<PostCategory> toAdd = newCategories.stream()
+                .filter(category -> !currentCategories.contains(category))
+                .toList();
+
+        // 실행
+        toRemove.forEach(this::removePostCategoryMapping);
+        toAdd.forEach(category -> new PostCategoryMapping(this, category));
     }
 
     /** 좋아요 수 증가 */
diff --git a/src/main/java/com/back/domain/board/post/service/PostService.java b/src/main/java/com/back/domain/board/post/service/PostService.java
index b5db7766..d290d819 100644
--- a/src/main/java/com/back/domain/board/post/service/PostService.java
+++ b/src/main/java/com/back/domain/board/post/service/PostService.java
@@ -49,17 +49,18 @@ public PostResponse createPost(PostRequest request, Long userId) {
         // Post 생성
         Post post = new Post(user, request.title(), request.content(), request.thumbnailUrl());
 
+        // Post 저장
+        Post saved = postRepository.save(post);
+
         // Category 매핑
         if (request.categoryIds() != null) {
             List<PostCategory> categories = postCategoryRepository.findAllById(request.categoryIds());
             if (categories.size() != request.categoryIds().size()) {
                 throw new CustomException(ErrorCode.CATEGORY_NOT_FOUND);
             }
-            post.updateCategories(categories);
+            saved.updateCategories(categories);
         }
 
-        // Post 저장 및 응답 반환
-        Post saved = postRepository.save(post);
         return PostResponse.from(saved);
     }