adding modified design.rb for sloving dup prob

app/models/design.rb

@@ -36,7 +36,9 @@ class Design
   def files=(attrs)
     files = eval(attrs.last)
     attrs[0].each do |a|
-      files.build(:file => a[:file], :to_save => true)
+      if(a[:id].nil?)
+        files.build(:file => a[:file], :to_save => true)
+      end
     end
   end