fix: getPostBy() does not return posts in subcategories (#2405)

#### What type of PR is this?

/kind bug
/area core

#### What this PR does / why we need it:

修改 PostCategoryServiceImpl.getPostBy() ，使其同时返回子分类文章。同时添加相关测试样例。

#### Which issue(s) this PR fixes:

Fixes #2368 

#### Special notes for your reviewer:

```release-note
修复在单个分类所属文章页面页面变量中无法获取子分类中文章的问题
```

src/main/java/run/halo/app/service/impl/PostCategoryServiceImpl.java

@@ -123,7 +123,11 @@ public class PostCategoryServiceImpl extends AbstractCrudService<PostCategory, I
         Assert.notNull(categoryId, "Category id must not be null");
 
         // Find all post ids
-        Set<Integer> postIds = postCategoryRepository.findAllPostIdsByCategoryId(categoryId);
+        Set<Integer> postIds = categoryService.listAllByParentId(categoryId)
+            .stream()
+            .map(item -> postCategoryRepository.findAllPostIdsByCategoryId(item.getId()))
+            .flatMap(Set::stream)
+            .collect(Collectors.toSet());
 
         return postRepository.findAllById(postIds);
     }
@@ -134,8 +138,11 @@ public class PostCategoryServiceImpl extends AbstractCrudService<PostCategory, I
         Assert.notNull(status, "Post status must not be null");
 
         // Find all post ids
-        Set<Integer> postIds =
+        Set<Integer> postIds = categoryService.listAllByParentId(categoryId)
-            postCategoryRepository.findAllPostIdsByCategoryId(categoryId, status);
+            .stream()
+            .map(item -> postCategoryRepository.findAllPostIdsByCategoryId(item.getId(), status))
+            .flatMap(Set::stream)
+            .collect(Collectors.toSet());
 
         return postRepository.findAllById(postIds);
     }
@@ -146,8 +153,11 @@ public class PostCategoryServiceImpl extends AbstractCrudService<PostCategory, I
         Assert.notNull(status, "Post status must not be null");
 
         // Find all post ids
-        Set<Integer> postIds = postCategoryRepository
+        Set<Integer> postIds = categoryService.listAllByParentId(categoryId)
-            .findAllPostIdsByCategoryId(categoryId, status);
+            .stream()
+            .map(item -> postCategoryRepository.findAllPostIdsByCategoryId(item.getId(), status))
+            .flatMap(Set::stream)
+            .collect(Collectors.toSet());
 
         return postRepository.findAllById(postIds);
     }
@@ -163,10 +173,13 @@ public class PostCategoryServiceImpl extends AbstractCrudService<PostCategory, I
             throw new NotFoundException("查询不到该分类的信息").setErrorData(slug);
         }
 
-        Set<Integer> postsIds = postCategoryRepository
+        Set<Integer> postIds = categoryService.listAllByParentId(category.getId())
-            .findAllPostIdsByCategoryId(category.getId(), status);
+            .stream()
+            .map(item -> postCategoryRepository.findAllPostIdsByCategoryId(item.getId(), status))
+            .flatMap(Set::stream)
+            .collect(Collectors.toSet());
 
-        return postRepository.findAllById(postsIds);
+        return postRepository.findAllById(postIds);
     }
 
     @Override
@@ -180,10 +193,13 @@ public class PostCategoryServiceImpl extends AbstractCrudService<PostCategory, I
             throw new NotFoundException("查询不到该分类的信息").setErrorData(slug);
         }
 
-        Set<Integer> postsIds =
+        Set<Integer> postIds = categoryService.listAllByParentId(category.getId())
-            postCategoryRepository.findAllPostIdsByCategoryId(category.getId(), status);
+            .stream()
+            .map(item -> postCategoryRepository.findAllPostIdsByCategoryId(item.getId(), status))
+            .flatMap(Set::stream)
+            .collect(Collectors.toSet());
 
-        return postRepository.findAllById(postsIds);
+        return postRepository.findAllById(postIds);
     }
 
     @Override

src/test/java/run/halo/app/service/impl/PostCategoryServiceImplTest.java

@@ -0,0 +1,147 @@
+package run.halo.app.service.impl;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import java.util.Set;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.jdbc.EmbeddedDatabaseConnection;
+import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase;
+import org.springframework.boot.test.context.SpringBootTest;
+import run.halo.app.model.entity.Category;
+import run.halo.app.model.entity.Post;
+import run.halo.app.model.entity.PostCategory;
+import run.halo.app.model.enums.PostStatus;
+import run.halo.app.service.CategoryService;
+
+@SpringBootTest
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+@AutoConfigureTestDatabase(connection = EmbeddedDatabaseConnection.H2)
+class PostCategoryServiceImplTest {
+
+    @Autowired
+    private CategoryService categoryService;
+
+    @Autowired
+    private PostCategoryServiceImpl postCategoryService;
+
+    @Autowired
+    private PostServiceImpl postService;
+
+    @BeforeAll
+    public void setUp() {
+        Category category1 = new Category();
+        category1.setId(1);
+        category1.setName("分类-1");
+        category1.setSlug("category-1");
+
+        Category category2 = new Category();
+        category2.setId(2);
+        category2.setName("分类-1-1");
+        category2.setSlug("category-1-1");
+        category2.setParentId(1);
+
+        Category category3 = new Category();
+        category3.setId(3);
+        category3.setName("分类-1-1-1");
+        category3.setSlug("category-1-1-1");
+        category3.setParentId(2);
+
+        Category category4 = new Category();
+        category4.setId(4);
+        category4.setName("分类-1-1-2");
+        category4.setSlug("category-1-1-2");
+        category4.setParentId(2);
+
+        categoryService.create(category1);
+        categoryService.create(category2);
+        categoryService.create(category3);
+        categoryService.create(category4);
+
+        Post post1 = new Post();
+        post1.setId(1);
+        post1.setTitle("post1");
+        post1.setSlug("post1");
+
+        Post post2 = new Post();
+        post2.setId(2);
+        post2.setTitle("post2");
+        post2.setSlug("post2");
+        post2.setStatus(PostStatus.PUBLISHED);
+
+        Post post3 = new Post();
+        post3.setId(3);
+        post3.setTitle("post3");
+        post3.setSlug("post3");
+        post3.setStatus(PostStatus.PUBLISHED);
+
+        Post post4 = new Post();
+        post4.setId(4);
+        post4.setTitle("post4");
+        post4.setSlug("post4");
+
+        postService.create(post1);
+        postService.create(post2);
+        postService.create(post3);
+        postService.create(post4);
+
+        PostCategory postCategory1 = new PostCategory();
+        postCategory1.setCategoryId(1);
+        postCategory1.setPostId(1);
+
+        PostCategory postCategory2 = new PostCategory();
+        postCategory2.setCategoryId(2);
+        postCategory2.setPostId(2);
+
+        PostCategory postCategory3 = new PostCategory();
+        postCategory3.setCategoryId(3);
+        postCategory3.setPostId(3);
+
+        PostCategory postCategory4 = new PostCategory();
+        postCategory4.setCategoryId(4);
+        postCategory4.setPostId(4);
+
+        postCategoryService.create(postCategory1);
+        postCategoryService.create(postCategory2);
+        postCategoryService.create(postCategory3);
+        postCategoryService.create(postCategory4);
+    }
+
+    @Test
+    void listPostByCategoryIdTest() {
+        List<Post> posts = postCategoryService.listPostBy(1);
+        assertEquals(List.of(postService.getById(1), postService.getById(2), postService.getById(3),
+            postService.getById(4)), posts);
+    }
+
+    @Test
+    void listPostByCategoryIdAndStatusTest() {
+        List<Post> posts = postCategoryService.listPostBy(1, PostStatus.PUBLISHED);
+        assertEquals(List.of(postService.getById(2), postService.getById(3)), posts);
+    }
+
+    @Test
+    void listPostByCategoryIdAndStatusesTest() {
+        List<Post> posts =
+            postCategoryService.listPostBy(1, Set.of(PostStatus.PUBLISHED, PostStatus.DRAFT));
+        assertEquals(List.of(postService.getById(1), postService.getById(2), postService.getById(3),
+            postService.getById(4)), posts);
+    }
+
+    @Test
+    void listPostBySlugIdAndStatusTest() {
+        List<Post> posts = postCategoryService.listPostBy("category-1", PostStatus.PUBLISHED);
+        assertEquals(List.of(postService.getById(2), postService.getById(3)), posts);
+    }
+
+    @Test
+    void listPostBySlugIdAndStatusesTest() {
+        List<Post> posts = postCategoryService.listPostBy("category-1",
+            Set.of(PostStatus.PUBLISHED, PostStatus.DRAFT));
+        assertEquals(List.of(postService.getById(1), postService.getById(2), postService.getById(3),
+            postService.getById(4)), posts);
+    }
+}