gistfile1.rb

require 'rubygems'
require 'dm-core'

DataMapper.setup(:default, "sqlite3:///#{File.expand_path(File.dirname(__FILE__))}/test.db")

class User
  include DataMapper::Resource
  property :id, Integer, :serial => true
  property :name, String, :nullable => false
  has n, :items
end

class Item
  include DataMapper::Resource
  property :id, Integer, :serial => true
  property :name, String, :nullable => false
  belongs_to :user
end

DataMapper.auto_migrate!