rails-acts_as_paranoid

参考
Github
Github for rails 3.1

1. installing

> vi Gemfile
-----
gem 'rails3_acts_as_paranoid', '~>0.1.4'
-----
:wq

> bundle
...
Installing rails3_acts_as_paranoid (0.1.4)
...
Your bundle is complete! ...

2. setting for migration

rails g migration AddDeletedAtToModel deleted_at:datetime
  invoke  active_record
  create    db/migrate/20120331022512_add_deleted_at_to_model.rb

> rake db:migrate

3. setting for model

vi app/models/modelname.rb
-----
class Modelname < ActiveRecord::Base
  acts_as_paranoid
end
-----
:wq

> rails server
* require reboots

done!

※一応動作確認出来ました。