Add 'revision' attribute to Conference, managed by an observer

app/models/revision_observer.rb

@@ -0,0 +1,26 @@
+#
+# suseconferenceclient relies on a 'revision' attribute for caching and
+# doing some calculations.
+#
+# It should be incremented after any change in the conference or in any
+# associated models
+#
+# This observer updates the revision column in a non-intrusive way,
+# preventing validations, callbacks or exceptions to be triggered
+#
+# Relying on paper_trail could also be an option, but a 'revision' column
+# in table 'conferences' looks like a more simple and straightforward solution
+#
+class RevisionObserver < ActiveRecord::Observer
+  observe :conference, :event, :room, :social_event, :track
+
+  def after_save(model)
+    begin
+      conference = model.kind_of?(Conference) ? model : model.conference
+      conference.reload.increment(:revision)
+      conference.update_column(:revision, conference.revision)
+    rescue
+      nil
+    end
+  end
+end