README

I needed a way to keep track of ActiveModel changes during a transaction and launch a Sidekiq job in after_commit if a value changes.

Alas:

• ActiveModel::Dirty.changes() isn't available in after_commit
• ActiveModel::Dirty.previous_changes() is available but it only reports the most recent save

I needed a more robust solution that keeps track of all the changes in the transaction -- even if the model was saved multiple times.

So I created this sample Rails app with an ActiveSupport::Concern called TrackSavedChanges where saved_changes() returns a single AR-style changes() hash that reflects the cumulative effect of a sequence of saves from the first to last. Consider this code:

after_commit: :after_commit_test

test = Test.create(number: 1, title: "1")
test = Test.find(test.id) # to initialize a fresh object

test.transaction do
  test.update(number: 2)
  test.update(title: "2")
end

def :after_commit_test
  puts previous_changes.inspect
  puts saved_changes.inspect
end

which results in:

previous_changes: {"title"=>["1", "2"], "updated_at"=>[...]}
saved_changes: {"title"=>["1", "2"], "number"=>[1, 2], "updated_at"=>[...]}

so that saved_changes also includes number which was omitted from previous_changes

To see the issue in action, clone this repo and running Test.test from inside the Rails console. For a deeper understanding see:

• Stack Overflow at http://stackoverflow.com/questions/7128073/after-commit-for-an-attribute
• Module code in track_saved_changes.rb
• Automated test in test_spec.rb

Enjoy!