资源缓存相关BUG修改

app/models/attachment.rb

@@ -686,9 +686,11 @@ class Attachment < ActiveRecord::Base
   #更新时间
   def update_others
     if self.course
+      if self.course.is_a?(::Course)
         self.course.update_course
       end
     end
+  end
 end
 
 # Delete the previous articles index in Elasticsearch