dmtest.rb

#!/usr/bin/env ruby -Ku
 
require 'rubygems'
require 'dm-core'
 
DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'mysql://localhost/testdb')
 
class User
  include DataMapper::Resource
 
  property :id, Serial
  property :name, String
  has 1, :address
end

class Address
  include DataMapper::Resource
  
  property :id, Serial
  property :country, String
  belongs_to :user
end
 
DataMapper.auto_migrate!

# Create a new user
u = User.new(:name => 'Bob')
p u.save    # => true

# Read the record back from the db
u = User.first

# Assign a new address to the user
u.address ||= Address.new   #  => runtime error