feat(service): 删除分组时更新相关文件

- 在删除分组前，将该分组下的所有文件移动到默认分组（ID为999）
- 新增 MarkdownFileMapper 依赖，用于更新文件分组
- 使用 @Transactional 注解确保删除分组和更新文件的操作在一个事务中完成

biji-houdaun/src/main/java/com/test/bijihoudaun/service/impl/GroupingServiceImpl.java

@@ -1,13 +1,17 @@
 package com.test.bijihoudaun.service.impl;
 
 import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
+import com.baomidou.mybatisplus.core.conditions.update.LambdaUpdateWrapper;
 import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
 import com.test.bijihoudaun.entity.Grouping;
+import com.test.bijihoudaun.entity.MarkdownFile;
 import com.test.bijihoudaun.mapper.GroupingMapper;
+import com.test.bijihoudaun.mapper.MarkdownFileMapper;
 import com.test.bijihoudaun.service.GroupingService;
 import com.test.bijihoudaun.util.SnowflakeIdGenerator;
 import jakarta.annotation.Resource;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
 
 import java.util.List;
 
@@ -19,6 +23,8 @@ public class GroupingServiceImpl
     @Resource
     private GroupingMapper groupingMapper;
     @Resource
+    private MarkdownFileMapper markdownFileMapper;
+    @Resource
     private SnowflakeIdGenerator snowflakeIdGenerator;
 
 
@@ -46,7 +52,13 @@ public class GroupingServiceImpl
     }
 
     @Override
+    @Transactional
     public void deleteGrouping(Long id) {
+        LambdaUpdateWrapper<MarkdownFile> updateWrapper = new LambdaUpdateWrapper<>();
+        updateWrapper.eq(MarkdownFile::getGroupingId, id)
+                .set(MarkdownFile::getGroupingId, 999L);
+        markdownFileMapper.update(null, updateWrapper);
+
         this.removeById(id);
     }