transactions.rb

#!/usr/bin/env ruby
require 'active_record'

ActiveRecord::Base.logger = Logger.new(STDERR)

ActiveRecord::Base.establish_connection(
  :adapter => "sqlite3",
  :database => ":memory:"
)

ActiveRecord::Schema.define do
  create_table :widgets do |table|
    table.column :name, :string
  end

  create_table :bits do |table|
    table.column :widget_id, :integer
    table.column :name, :string
  end
end

class Widget < ActiveRecord::Base
  has_many :bits
  after_commit :let_me_know

  def let_me_know
    puts "I, widget #{name}, have changed."
  end
end

class Bit < ActiveRecord::Base
  belongs_to :widget, touch: true
end


Widget.create(name: 'Master P') # => I, widget Master P, have changed.

Widget.first.save # => I, widget Master P, have changed.

Widget.first.bits.create(name: 'shoelace') # => I, widget Master P, have changed.

ActiveRecord::Base.transaction do
  20.times { |x| Bit.create(widget_id: 1, name: "strap-#{x}") }
end # => I, wiget Master P, have changed.