[1] Materialized Path 무한 댓글 조회

src/main/java/ex/demo/Comment.java

@@ -0,0 +1,41 @@
+package ex.demo;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+import java.time.LocalDateTime;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+@Entity
+@Table(name = "comments")
+@Getter
+@NoArgsConstructor
+@AllArgsConstructor
+public class Comment {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+    private Long postId;
+    private Long parentId;
+    private int depth;
+    private String content;
+    private LocalDateTime createdAt;
+
+    // Materialized Path
+    @Column(nullable = false, length = 255)
+    private String path;
+
+    public Comment(Long postId, Long parentId, int depth, String content, String parentPath, int position) {
+        this.postId = postId;
+        this.parentId = parentId;
+        this.depth = depth;
+        this.content = content;
+        this.createdAt = LocalDateTime.now();
+        this.path = (parentPath == null ? "" : parentPath + "/") + String.format("%05d", position);
+    }
+}

src/main/java/ex/demo/CommentController.java

@@ -0,0 +1,51 @@
+package ex.demo;
+
+import jakarta.validation.Valid;
+import java.util.List;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/api/comments")
+@RequiredArgsConstructor
+public class CommentController {
+
+    private final CommentService commentService;
+
+    @PostMapping
+    public ResponseEntity<CommentDto> createComment(
+            @Valid @RequestBody CommentCreateRequest request) {
+        CommentDto comment = commentService.createComment(request);
+        return ResponseEntity.ok(comment);
+    }
+
+    // 커서 기반 페이지네이션: lastPath 파라미터 사용
+    @GetMapping
+    public ResponseEntity<List<CommentDto>> getComments(
+            @RequestParam Long postId,
+            @RequestParam(required = false) String lastPath,
+            @RequestParam(defaultValue = "10") int size) {
+        List<CommentDto> comments = commentService.getComments(postId, lastPath, size);
+        return ResponseEntity.ok(comments);
+    }
+
+    @GetMapping("/count")
+    public ResponseEntity<Long> getCommentCount(@RequestParam Long postId) {
+        long count = commentService.getCommentCount(postId);
+        return ResponseEntity.ok(count);
+    }
+
+    @DeleteMapping("/{commentId}")
+    public ResponseEntity<Void> deleteComment(@PathVariable Long commentId) {
+        commentService.deleteComment(commentId);
+        return ResponseEntity.noContent().build();
+    }
+}

src/main/java/ex/demo/CommentCreateRequest.java

@@ -0,0 +1,11 @@
+package ex.demo;
+
+import lombok.Getter;
+
+@Getter
+public class CommentCreateRequest {
+    private Long postId;
+    private String content;
+    private Long parentId; // null이면 최상위 댓글
+}
+

src/main/java/ex/demo/CommentDto.java

@@ -0,0 +1,18 @@
+package ex.demo;
+
+import lombok.Builder;
+import lombok.Getter;
+import java.time.LocalDateTime;
+
+@Getter
+@Builder
+public class CommentDto {
+    private Long id;
+    private Long postId;
+    private String content;
+    private Long parentId;
+    private int depth;
+    private String path; // Materialized Path
+    private LocalDateTime createdAt;
+}
+

src/main/java/ex/demo/CommentRepository.java

@@ -0,0 +1,38 @@
+package ex.demo;
+
+import jakarta.persistence.LockModeType;
+import java.util.List;
+import java.util.Optional;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Lock;
+import org.springframework.data.jpa.repository.Query;
+
+public interface CommentRepository extends JpaRepository<Comment, Long> {
+    // 커서 기반 페이지네이션 (path 기준)
+    List<Comment> findByPostIdAndPathGreaterThanOrderByPathAsc(Long postId, String lastPath, Pageable pageable);
+
+    // 첫 페이지 조회 (lastPath 없이)
+    List<Comment> findByPostIdOrderByPathAsc(Long postId, Pageable pageable);
+
+    // 같은 부모 아래 형제들의 최대 position 조회 (동시성 처리)
+    @Lock(LockModeType.PESSIMISTIC_WRITE)
+    @Query("""
+            SELECT COALESCE(MAX(CAST(SUBSTRING(c.path, LENGTH(:prefix) + 2, 5) AS int)), 0)
+            FROM Comment c
+            WHERE c.postId = :postId
+              AND (:prefix = '' AND c.parentId IS NULL
+                   OR c.path LIKE CONCAT(:prefix, '/%'))
+            """)
+    int findMaxPositionByPostIdAndPrefixForUpdate(
+            Long postId,
+            String prefix
+    );
+
+    Optional<Comment> findByIdAndPostId(Long id, Long postId);
+
+    long countByPostId(Long postId);
+
+    // 서브트리 삭제용
+    void deleteByPostIdAndPathStartingWith(Long postId, String pathPrefix);
+}

src/main/java/ex/demo/CommentService.java

@@ -0,0 +1,90 @@
+package ex.demo;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import lombok.RequiredArgsConstructor;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@RequiredArgsConstructor
+@Transactional(readOnly = true)
+public class CommentService {
+
+    private final CommentRepository commentRepository;
+    private static final int MAX_DEPTH = 50;
+
+    @Transactional
+    public CommentDto createComment(CommentCreateRequest request) {
+        if (request.getParentId() == null) {
+            return addRootComment(request.getPostId(), request.getContent());
+        } else {
+            return addReply(request.getPostId(), request.getParentId(), request.getContent());
+        }
+    }
+
+    @Transactional
+    public CommentDto addRootComment(Long postId, String content) {
+        String prefix = "";
+        int maxPos = commentRepository.findMaxPositionByPostIdAndPrefixForUpdate(postId, prefix);
+        int newPos = maxPos + 1;
+        // 루트 댓글: parentId=null, parentPath=null
+        Comment comment = new Comment(postId, null, 0, content, null, newPos);
+        comment = commentRepository.save(comment);
+        return toDto(comment);
+    }
+
+    @Transactional
+    public CommentDto addReply(Long postId, Long parentId, String content) {
+        Comment parent = commentRepository.findByIdAndPostId(parentId, postId)
+                .orElseThrow(() -> new IllegalArgumentException("부모 댓글 없음"));
+        if (parent.getDepth() >= MAX_DEPTH) {
+            throw new IllegalArgumentException("최대 깊이 초과");
+        }
+        String prefix = parent.getPath();
+        int maxPos = commentRepository.findMaxPositionByPostIdAndPrefixForUpdate(postId, prefix);
+        int newPos = maxPos + 1;
+        Comment comment = new Comment(postId, parentId, parent.getDepth() + 1, content, prefix, newPos);
+        comment = commentRepository.save(comment);
+        return toDto(comment);
+    }
+
+    // 커서 기반 페이지네이션
+    public List<CommentDto> getComments(Long postId, String lastPath, int size) {
+        Pageable pageable = PageRequest.of(0, size);
+        List<Comment> comments;
+        if (lastPath == null || lastPath.isEmpty()) {
+            comments = commentRepository.findByPostIdOrderByPathAsc(postId, pageable);
+        } else {
+            comments = commentRepository.findByPostIdAndPathGreaterThanOrderByPathAsc(postId, lastPath, pageable);
+        }
+        return comments.stream().map(this::toDto).collect(Collectors.toList());
+    }
+
+    public long getCommentCount(Long postId) {
+        return commentRepository.countByPostId(postId);
+    }
+
+    @Transactional
+    public void deleteComment(Long commentId) {
+        Comment target = commentRepository.findById(commentId)
+                .orElseThrow(() -> new IllegalArgumentException("댓글 없음"));
+        String prefix = target.getPath() + "/";
+        commentRepository.deleteByPostIdAndPathStartingWith(target.getPostId(), prefix);
+        commentRepository.delete(target);
+    }
+
+    private CommentDto toDto(Comment comment) {
+        return CommentDto.builder()
+                .id(comment.getId())
+                .postId(comment.getPostId())
+                .content(comment.getContent())
+                .parentId(comment.getParentId())
+                .depth(comment.getDepth())
+                .createdAt(comment.getCreatedAt())
+                .path(comment.getPath())
+                .build();
+    }
+}

src/main/java/ex/demo/DemoApplication.java

@@ -6,8 +6,8 @@
 @SpringBootApplication
 public class DemoApplication {
 
-	public static void main(String[] args) {
-		SpringApplication.run(DemoApplication.class, args);
-	}
+    public static void main(String[] args) {
+        SpringApplication.run(DemoApplication.class, args);
+    }
 
 }

src/main/java/ex/demo/Post.java

@@ -0,0 +1,29 @@
+package ex.demo;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+@Entity
+@Getter
+@AllArgsConstructor
+@Setter
+@NoArgsConstructor
+public class Post {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String title;
+    private String content;
+
+    public Post(String title, String content) {
+        this.title = title;
+        this.content = content;
+    }
+}

src/main/java/ex/demo/PostRepository.java

@@ -0,0 +1,7 @@
+package ex.demo;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface PostRepository extends JpaRepository<Post, Long> {
+    // 추가적인 쿼리 메서드가 필요하면 여기에 정의
+}