Refactor Chunk API (#2855)

### What problem does this PR solve?

Refactor Chunk API
#2846
### Type of change


- [x] Refactoring

---------

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

api/db/services/document_service.py

@@ -61,14 +61,13 @@ class DocumentService(CommonService):
             docs = docs.where(
                 fn.LOWER(cls.model.name).contains(keywords.lower())
             )
-        count = docs.count()
         if desc:
             docs = docs.order_by(cls.model.getter_by(orderby).desc())
         else:
             docs = docs.order_by(cls.model.getter_by(orderby).asc())
 
         docs = docs.paginate(page_number, items_per_page)
-
+        count = docs.count()
         return list(docs.dicts()), count