Feat: 게시글 생성 API 구현

Author: joyewon0705

src/main/java/com/back/domain/board/controller/PostController.java

@@ -0,0 +1,35 @@
+package com.back.domain.board.controller;
+
+import com.back.domain.board.dto.PostRequest;
+import com.back.domain.board.dto.PostResponse;
+import com.back.domain.board.service.PostService;
+import com.back.global.common.dto.RsData;
+import com.back.global.security.user.CustomUserDetails;
+import jakarta.validation.Valid;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping("/api/posts")
+@RequiredArgsConstructor
+public class PostController {
+    private final PostService postService;
+
+    // 게시글 생성
+    @PostMapping
+    public ResponseEntity<RsData<PostResponse>> createPost(
+            @RequestBody @Valid PostRequest request,
+            @AuthenticationPrincipal CustomUserDetails user
+    ) {
+        PostResponse response = postService.createPost(request, user.getUserId());
+        return ResponseEntity
+                .status(HttpStatus.CREATED)
+                .body(RsData.success(
+                        "게시글이 생성되었습니다.",
+                        response
+                ));
+    }
+}

src/main/java/com/back/domain/board/dto/AuthorResponse.java

@@ -0,0 +1,21 @@
+package com.back.domain.board.dto;
+
+import com.back.domain.user.entity.User;
+
+/**
+ * 작성자 응답 DTO
+ *
+ * @param id       작성자 ID
+ * @param nickname 작성자 닉네임
+ */
+public record AuthorResponse(
+        Long id,
+        String nickname
+) {
+    public static AuthorResponse from(User user) {
+        return new AuthorResponse(
+                user.getId(),
+                user.getUserProfile().getNickname()
+        );
+    }
+}

src/main/java/com/back/domain/board/dto/CategoryResponse.java

@@ -0,0 +1,21 @@
+package com.back.domain.board.dto;
+
+import com.back.domain.board.entity.PostCategory;
+
+/**
+ * 카테고리 응답 DTO
+ *
+ * @param id    카테고리 ID
+ * @param name  카테고리 이름
+ */
+public record CategoryResponse(
+        Long id,
+        String name
+) {
+    public static CategoryResponse from(PostCategory category) {
+        return new CategoryResponse(
+                category.getId(),
+                category.getName()
+        );
+    }
+}

src/main/java/com/back/domain/board/dto/PostRequest.java

@@ -0,0 +1,18 @@
+package com.back.domain.board.dto;
+
+import jakarta.validation.constraints.NotBlank;
+
+import java.util.List;
+
+/**
+ * 게시글 생성 및 수정을 위한 요청 DTO
+ *
+ * @param title         게시글 제목
+ * @param content       게시글 내용
+ * @param categoryIds   카테고리 ID 리스트
+ */
+public record PostRequest(
+        @NotBlank String title,
+        @NotBlank String content,
+        List<Long> categoryIds
+) {}

src/main/java/com/back/domain/board/dto/PostResponse.java

@@ -0,0 +1,40 @@
+package com.back.domain.board.dto;
+
+import com.back.domain.board.entity.Post;
+import java.time.LocalDateTime;
+import java.util.List;
+
+/**
+ * 게시글 응답 DTO
+ *
+ * @param postId     게시글 ID
+ * @param author     작성자 정보
+ * @param title      게시글 제목
+ * @param content    게시글 내용
+ * @param categories   게시글 카테고리 목록
+ * @param createdAt  게시글 생성 일시
+ * @param updatedAt  게시글 수정 일시
+ */
+public record PostResponse(
+        Long postId,
+        AuthorResponse author,
+        String title,
+        String content,
+        List<CategoryResponse> categories,
+        LocalDateTime createdAt,
+        LocalDateTime updatedAt
+) {
+    public static PostResponse from(Post post) {
+        return new PostResponse(
+                post.getId(),
+                AuthorResponse.from(post.getUser()),
+                post.getTitle(),
+                post.getContent(),
+                post.getCategories().stream()
+                        .map(CategoryResponse::from)
+                        .toList(),
+                post.getCreatedAt(),
+                post.getUpdatedAt()
+        );
+    }
+}

src/main/java/com/back/domain/board/entity/Post.java

@@ -32,4 +32,28 @@ public class Post extends BaseEntity {
 
     @OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
     private List<Comment> comments = new ArrayList<>();
+
+    // -------------------- 생성자 --------------------
+    public Post(User user, String title, String content) {
+        this.user = user;
+        this.title = title;
+        this.content = content;
+    }
+
+    // -------------------- 비즈니스 메서드 --------------------
+    // 카테고리 업데이트
+    public void updateCategories(List<PostCategory> categories) {
+        this.postCategoryMappings.clear();
+        categories.forEach(category ->
+                this.postCategoryMappings.add(new PostCategoryMapping(this, category))
+        );
+    }
+
+    // -------------------- 헬퍼 메서드 --------------------
+    // 게시글에 연결된 카테고리 목록 조회
+    public List<PostCategory> getCategories() {
+        return postCategoryMappings.stream()
+                .map(PostCategoryMapping::getCategory)
+                .toList();
+    }
 }

src/main/java/com/back/domain/board/entity/PostCategoryMapping.java

@@ -18,4 +18,10 @@ public class PostCategoryMapping {
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "category_id")
     private PostCategory category;
+
+    // -------------------- 생성자 --------------------
+    public PostCategoryMapping(Post post, PostCategory category) {
+        this.post = post;
+        this.category = category;
+    }
 }

src/main/java/com/back/domain/board/repository/PostCategoryRepository.java

@@ -0,0 +1,9 @@
+package com.back.domain.board.repository;
+
+import com.back.domain.board.entity.PostCategory;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface PostCategoryRepository extends JpaRepository<PostCategory, Long> {
+}

src/main/java/com/back/domain/board/repository/PostRepository.java

@@ -0,0 +1,9 @@
+package com.back.domain.board.repository;
+
+import com.back.domain.board.entity.Post;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface PostRepository extends JpaRepository<Post, Long> {
+}

src/main/java/com/back/domain/board/service/PostService.java

@@ -0,0 +1,56 @@
+package com.back.domain.board.service;
+
+import com.back.domain.board.dto.PostRequest;
+import com.back.domain.board.dto.PostResponse;
+import com.back.domain.board.entity.Post;
+import com.back.domain.board.entity.PostCategory;
+import com.back.domain.board.repository.PostCategoryRepository;
+import com.back.domain.board.repository.PostRepository;
+import com.back.domain.user.entity.User;
+import com.back.domain.user.repository.UserRepository;
+import com.back.global.exception.CustomException;
+import com.back.global.exception.ErrorCode;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+
+@Service
+@RequiredArgsConstructor
+@Transactional
+public class PostService {
+    private final PostRepository postRepository;
+    private final UserRepository userRepository;
+    private final PostCategoryRepository postCategoryRepository;
+
+    /**
+     * 게시글 생성 서비스
+     * 1. User 조회
+     * 2. Post 생성
+     * 3. Category 매핑
+     * 4. Post 저장 및 PostResponse 반환
+     */
+    public PostResponse createPost(PostRequest request, Long userId) {
+
+        // User 조회
+        User user = userRepository.findById(userId)
+                .orElseThrow(() -> new CustomException(ErrorCode.USER_NOT_FOUND));
+
+        // Post 생성
+        Post post = new Post(user, request.title(), request.content());
+
+        // 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);
+        }
+
+        // Post 저장 및 응답 반환
+        Post saved = postRepository.save(post);
+        return PostResponse.from(saved);
+    }
+}