Gemfile.rb

DATAMAPPER = 'git://github.com/datamapper'
DM_VERSION = '~> 1.0.0.rc3'
DO_VERSION = '~> 0.10.3'

gem 'dm-sqlite-adapter',    DM_VERSION, :git => "#{DATAMAPPER}/dm-sqlite-adapter.git"
gem 'dm-validations',       DM_VERSION, :git => "#{DATAMAPPER}/dm-validations"
gem 'dm-constraints',       DM_VERSION, :git => "#{DATAMAPPER}/dm-constraints"
gem 'dm-aggregates',        DM_VERSION, :git => "#{DATAMAPPER}/dm-aggregates"
gem 'dm-is-list',           DM_VERSION, :git => "#{DATAMAPPER}/dm-is-list"

gem 'dm-core',              DM_VERSION, :git => "#{DATAMAPPER}/dm-core.git"
gem 'dm-do-adapter',        DM_VERSION, :git => "#{DATAMAPPER}/dm-do-adapter"
gem 'dm-active_model',      DM_VERSION, :git => "#{DATAMAPPER}/dm-active_model"

gem 'data_objects',         DO_VERSION, :git => "#{DATAMAPPER}/do.git"
gem 'do_sqlite3',           DO_VERSION, :git => "#{DATAMAPPER}/do.git"

test.rb

require 'rubygems'
require 'bundler'

Bundler.setup
Bundler.require :default

DataMapper.setup(:default, 'sqlite3::memory:')

class Candy
  include DataMapper::Resource
  include DataMapper::Validate
  
  property :id,   Serial
  property :name, String, :length => 1..20
  is :list
end

Candy.auto_migrate!
c = Candy.new

if c.save
  puts 'Saved'
else
  # this gives: 'Position must not be blank'
  puts 'Could not save because:'
  puts '  ' + c.errors.full_messages.join("\n  ")
end