Index: /home/pic/vc/playground/ror/playground/vendor/plugins/restful-rails/lib/http/conditions.rb
===================================================================
--- /home/pic/vc/playground/ror/playground/vendor/plugins/restful-rails/lib/http/conditions.rb	(revision 28)
+++ /home/pic/vc/playground/ror/playground/vendor/plugins/restful-rails/lib/http/conditions.rb	(working copy)
@@ -15,6 +15,10 @@
     end
 
     alias_method '<<', :push
+    
+    def consider_for_etag
+      @consider_for_etag ||= []
+    end
 
     def test!
       return unless @models.size > 0
@@ -31,7 +35,10 @@
         end
       end
 
-      response.etag          = Digest::MD5.hexdigest(lock_versions.join('|'))
+      #response.etag          = Digest::MD5.hexdigest(lock_versions.join('|'))
+      print "--> #{consider_for_etag}\n"
+      etag_values = [].concat(consider_for_etag).concat(lock_versions)
+      response.etag          = Digest::MD5.hexdigest(etag_values.join('|'))
       response.last_modified = updated_at_dates.compact.sort.last || Time.now
 
       raise HTTP::PreconditionFailedError                                                          unless match? || unmodified_since?