From d648ab7cb5277ac47bf57911e4d143bab89454c1 Mon Sep 17 00:00:00 2001
From: Ancor Gonzalez Sosa <ancor@suse.de>
Date: Mon, 8 Jul 2013 10:03:03 +0200
Subject: [PATCH] Add 'revision' attribute to Conference, managed by an
 observer

---
 app/models/revision_observer.rb               | 26 +++++++++++++++++++
 config/application.rb                         |  1 +
 ...130705055128_add_revision_to_conference.rb |  5 ++++
 db/schema.rb                                  |  3 ++-
 4 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 app/models/revision_observer.rb
 create mode 100644 db/migrate/20130705055128_add_revision_to_conference.rb

diff --git a/app/models/revision_observer.rb b/app/models/revision_observer.rb
new file mode 100644
index 00000000..7247efc0
--- /dev/null
+++ b/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
diff --git a/config/application.rb b/config/application.rb
index 76448fbb..4c76b590 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -25,6 +25,7 @@ module Osem
 
     # Activate observers that should always be running.
     # config.active_record.observers = :cacher, :garbage_collector, :forum_observer
+    config.active_record.observers = :revision_observer
 
     # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
     # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
diff --git a/db/migrate/20130705055128_add_revision_to_conference.rb b/db/migrate/20130705055128_add_revision_to_conference.rb
new file mode 100644
index 00000000..728b6551
--- /dev/null
+++ b/db/migrate/20130705055128_add_revision_to_conference.rb
@@ -0,0 +1,5 @@
+class AddRevisionToConference < ActiveRecord::Migration
+  def change
+    add_column :conferences, :revision, :integer
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 9acc0c8f..49028ecf 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20130626095459) do
+ActiveRecord::Schema.define(:version => 20130705055128) do
 
   create_table "call_for_papers", :force => true do |t|
     t.date     "start_date",    :null => false
@@ -62,6 +62,7 @@ ActiveRecord::Schema.define(:version => 20130626095459) do
     t.datetime "logo_updated_at"
     t.boolean  "use_dietary_choices",     :default => false
     t.boolean  "use_supporter_levels",    :default => false
+    t.integer  "revision"
   end
 
   create_table "dietary_choices", :force => true do |t|