gistfile1.rb

require 'rubygems'
require 'dm-core'

DataMapper.setup(:default, "mysql://root@localhost/dm_core_test")

class Order
  include DataMapper::Resource
  property :id, Serial

  has n, :events
end

class Event
  include DataMapper::Resource
  property :id, Serial
  property :title, String, :length => 255

  belongs_to :order
end

DataMapper.auto_migrate!

o = Order.new
e = o.events.new

o.save
puts o.id
puts e.order_id

e.reload
puts e.order_id