ar_after_transaction's Introduction

Do something only after the currently open transactions have finished.

Normally everything gets rolled back when a transaction fails, but you cannot roll back sending an email or adding a job to Resque.

Install

gem install ar_after_transaction

Usage

just-in-time callbacks

class User
  after_create :do_stuff, :oops

  def do_stuff
    after_transaction do
      send_an_email # cannot be rolled back
    end
    comments.create(...) # will be rolled back
  end

  def oops
    raise "do the rolback!"
  end
end

General 'this should be rolled back when in a transaction' code like jobs

class Resque
  def revertable_enqueue(*args)
    ActiveRecord::Base.after_transaction do
      enqueue(*args)
    end
  end
end

When not in a transaction

after_transaction will perform the given block immediately

Transactional fixtures <-> normally_open_transactions

after_transaction assumes zero open transactions.
If you use transactional fixtures you should change it in test mode.

# config/environments/test.rb
config.after_initialize do
  ActiveRecord::Base.normally_open_transactions = 1
end

Rails 3: after_commit hook can replace the first usage example:

class User
  after_commit :send_an_email :on=>:create
  after_create :do_stuff, :oops
  ...
end

Alternative

Rails 3+

basic support is built in, use it if you can!
after_commit :foo
after_commit :bar, :on => :create / :update

after_commit

pro: threadsafe
pro: more fine-grained callbacks (before_commit, after_commit, before_rollback, after_rollback)
con: doesn't let you define after_transaction callbacks anywhere like ar_after_transaction does (outside of the after_commit, etc. callbacks which only happen at certain points in the model's life cycle)
con: more complex