diff --git a/app/controllers/homework_attach_controller.rb b/app/controllers/homework_attach_controller.rb
index 4b7fdb15e..42c7ffc77 100644
--- a/app/controllers/homework_attach_controller.rb
+++ b/app/controllers/homework_attach_controller.rb
@@ -227,7 +227,7 @@ class HomeworkAttachController < ApplicationController
   def create
     bid = Bid.find params[:bid_id]
     if User.current.admin? || User.current.member_of_course?(bid.courses.first)   # modify by nwb
-      if bid.homeworks.where("user_id = ?",User.current).count == 0
+      if bid.homeworks.where("user_id = ?",User.current).empty?
         user_id = params[:user_id]
         bid_id = params[:bid_id]
         if params[:homework_attach]