in design,after online editing,return json url,callback not finish

app/controllers/admin/designs_controller.rb

@@ -30,18 +30,18 @@ class Admin::DesignsController < ApplicationController
     file_to_removed = files.find{ |obj|
       obj.file_filename == filename
     }
-    type = file_to_removed._type 
+    type = file_to_removed._type
+    new_file = ""
     Dir.mktmpdir('design_temp'){ |dir|
       temp_file = File.new(dir+'/'+filename,'w+')
       temp_file.write params[:context]
       replace_target = eval("@design.#{type.downcase.pluralize}")
-      a = replace_target.build(:file => temp_file,:to_save=>true)
-      debugger
+      new_file = replace_target.build(:file => temp_file,:to_save=>true)
       file_to_removed.destroy
       @design.save
-      debugger
       temp_file.close
-    }
+      }
+      render :json => new_file.file.url
     
   end