附件下载更新

app/controllers/attachments_controller.rb

@@ -286,7 +286,7 @@ private
     raise ActiveRecord::RecordNotFound if params[:filename] && params[:filename] != @attachment.filename
     if @attachment.container_type == 'Course'
       @course = @attachment.course
-    elsif @attachment.container.course
+    elsif @attachment.container.has_attribute?(:course) && @attachment.container.course
       @course = @attachment.container.course
     else
       unless @attachment.container_type == 'Bid' || @attachment.container_type == 'HomeworkAttach' || @attachment.container_type == 'Memo' || @attachment.container_type == 'Softapplication'