Add endpoints to list posts by tags and categories

src/main/java/com/openisle/controller/CategoryController.java

@@ -2,6 +2,7 @@ package com.openisle.controller;
 
 import com.openisle.model.Category;
 import com.openisle.service.CategoryService;
+import com.openisle.service.PostService;
 import lombok.Data;
 import lombok.RequiredArgsConstructor;
 import org.springframework.web.bind.annotation.*;
@@ -14,6 +15,7 @@ import java.util.stream.Collectors;
 @RequiredArgsConstructor
 public class CategoryController {
     private final CategoryService categoryService;
+    private final PostService postService;
 
     @PostMapping
     public CategoryDto create(@RequestBody CategoryRequest req) {
@@ -38,6 +40,21 @@ public class CategoryController {
         return toDto(categoryService.getCategory(id));
     }
 
+    @GetMapping("/{id}/posts")
+    public List<PostSummaryDto> listPostsByCategory(@PathVariable Long id,
+                                                    @RequestParam(value = "page", required = false) Integer page,
+                                                    @RequestParam(value = "pageSize", required = false) Integer pageSize) {
+        return postService.listPostsByCategories(java.util.List.of(id), page, pageSize)
+                .stream()
+                .map(p -> {
+                    PostSummaryDto dto = new PostSummaryDto();
+                    dto.setId(p.getId());
+                    dto.setTitle(p.getTitle());
+                    return dto;
+                })
+                .collect(Collectors.toList());
+    }
+
     private CategoryDto toDto(Category c) {
         CategoryDto dto = new CategoryDto();
         dto.setId(c.getId());
@@ -61,4 +78,10 @@ public class CategoryController {
         private String describe;
         private String icon;
     }
+
+    @Data
+    private static class PostSummaryDto {
+        private Long id;
+        private String title;
+    }
 }

src/main/java/com/openisle/controller/PostController.java

@@ -52,12 +52,23 @@ public class PostController {
     @GetMapping
     public List<PostDto> listPosts(@RequestParam(value = "categoryId", required = false) Long categoryId,
                                    @RequestParam(value = "categoryIds", required = false) List<Long> categoryIds,
+                                   @RequestParam(value = "tagId", required = false) Long tagId,
+                                   @RequestParam(value = "tagIds", required = false) List<Long> tagIds,
                                    @RequestParam(value = "page", required = false) Integer page,
                                    @RequestParam(value = "pageSize", required = false) Integer pageSize) {
         List<Long> ids = categoryIds;
         if (categoryId != null) {
             ids = java.util.List.of(categoryId);
         }
+        if ((tagId != null || (tagIds != null && !tagIds.isEmpty()))) {
+            List<Long> tids = tagIds;
+            if (tagId != null) {
+                tids = java.util.List.of(tagId);
+            }
+            return postService.listPostsByTags(tids, page, pageSize)
+                    .stream().map(this::toDto).collect(Collectors.toList());
+        }
+
         return postService.listPostsByCategories(ids, page, pageSize)
                 .stream().map(this::toDto).collect(Collectors.toList());
     }

src/main/java/com/openisle/controller/TagController.java

@@ -2,6 +2,7 @@ package com.openisle.controller;
 
 import com.openisle.model.Tag;
 import com.openisle.service.TagService;
+import com.openisle.service.PostService;
 import lombok.Data;
 import lombok.RequiredArgsConstructor;
 import org.springframework.web.bind.annotation.*;
@@ -14,6 +15,7 @@ import java.util.stream.Collectors;
 @RequiredArgsConstructor
 public class TagController {
     private final TagService tagService;
+    private final PostService postService;
 
     @PostMapping
     public TagDto create(@RequestBody TagRequest req) {
@@ -38,6 +40,21 @@ public class TagController {
         return toDto(tagService.getTag(id));
     }
 
+    @GetMapping("/{id}/posts")
+    public List<PostSummaryDto> listPostsByTag(@PathVariable Long id,
+                                               @RequestParam(value = "page", required = false) Integer page,
+                                               @RequestParam(value = "pageSize", required = false) Integer pageSize) {
+        return postService.listPostsByTags(java.util.List.of(id), page, pageSize)
+                .stream()
+                .map(p -> {
+                    PostSummaryDto dto = new PostSummaryDto();
+                    dto.setId(p.getId());
+                    dto.setTitle(p.getTitle());
+                    return dto;
+                })
+                .collect(Collectors.toList());
+    }
+
     private TagDto toDto(Tag tag) {
         TagDto dto = new TagDto();
         dto.setId(tag.getId());
@@ -61,4 +78,10 @@ public class TagController {
         private String describe;
         private String icon;
     }
+
+    @Data
+    private static class PostSummaryDto {
+        private Long id;
+        private String title;
+    }
 }

src/main/java/com/openisle/repository/PostRepository.java

@@ -4,6 +4,7 @@ import com.openisle.model.Post;
 import com.openisle.model.PostStatus;
 import com.openisle.model.User;
 import com.openisle.model.Category;
+import com.openisle.model.Tag;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaRepository;
 
@@ -15,6 +16,8 @@ public interface PostRepository extends JpaRepository<Post, Long> {
     List<Post> findByAuthorAndStatusOrderByCreatedAtDesc(User author, PostStatus status, Pageable pageable);
     List<Post> findByCategoryInAndStatus(List<Category> categories, PostStatus status);
     List<Post> findByCategoryInAndStatus(List<Category> categories, PostStatus status, Pageable pageable);
+    List<Post> findDistinctByTagsInAndStatus(List<Tag> tags, PostStatus status);
+    List<Post> findDistinctByTagsInAndStatus(List<Tag> tags, PostStatus status, Pageable pageable);
     List<Post> findByTitleContainingIgnoreCaseOrContentContainingIgnoreCaseAndStatus(String titleKeyword, String contentKeyword, PostStatus status);
     List<Post> findByContentContainingIgnoreCaseAndStatus(String keyword, PostStatus status);
     List<Post> findByTitleContainingIgnoreCaseAndStatus(String keyword, PostStatus status);

src/main/java/com/openisle/service/PostService.java

@@ -106,6 +106,29 @@ public class PostService {
         return postRepository.findByAuthorAndStatusOrderByCreatedAtDesc(user, PostStatus.PUBLISHED, pageable);
     }
 
+    public List<Post> listPostsByTags(java.util.List<Long> tagIds,
+                                      Integer page,
+                                      Integer pageSize) {
+        if (tagIds == null || tagIds.isEmpty()) {
+            return java.util.List.of();
+        }
+
+        Pageable pageable = null;
+        if (page != null && pageSize != null) {
+            pageable = PageRequest.of(page, pageSize);
+        }
+
+        java.util.List<com.openisle.model.Tag> tags = tagRepository.findAllById(tagIds);
+        if (tags.isEmpty()) {
+            return java.util.List.of();
+        }
+
+        if (pageable != null) {
+            return postRepository.findDistinctByTagsInAndStatus(tags, PostStatus.PUBLISHED, pageable);
+        }
+        return postRepository.findDistinctByTagsInAndStatus(tags, PostStatus.PUBLISHED);
+    }
+
     public List<Post> listPendingPosts() {
         return postRepository.findByStatus(PostStatus.PENDING);
     }