_setup.sh

rails new abcdefg -m http://datamapper.org/templates/rails.rb --skip-test-unit
cd abcdefg
# copy gemfile from this gist
wget https://raw.github.com/gist/1011318/56a64b96b329215697b78481c6b45463931eae6f/Gemfile -O Gemfile

bundle
rails g rspec:install

# Copy from this gist:
# config/application.rb
# spec/spec_helper.rb
# app/models/user.rb
# app/models/friendship.rb
# app/models/friendship_request.rb
# spec/models/friendship_spec.rb
wget https://raw.github.com/gist/1011318/10930a20546028381020153a7b271e3f4d6bec2f/application.rb -O config/application.rb

wget https://raw.github.com/gist/1011318/4f1a09637d1dd1262f0a450769ccadb1d80784e0 -O spec/spec_helper.rb

wget https://raw.github.com/gist/1011318/5d64a67165fe9919f057341d2605cadc63119afd -O app/models/friendship.rb

wget https://raw.github.com/gist/1011318/406a21d508bf395ab09930329574b0f9ff431a23 -O app/models/friendship_request.rb

wget https://raw.github.com/gist/1011318/13e7e2169b5c85bfa58bc55c77113c11bb89b6e1 -O app/models/user.rb

mkdir spec/models
wget https://raw.github.com/gist/1011318/86cfbdc3f853deed69bbbdc022a9e5fd3c092d07 -O spec/models/friendship_spec.rb

rspec spec/models/friendship_spec.rb

app_models_friendship.rb

class Friendship
	include DataMapper::Resource

	belongs_to :user,	'User', :key => true
	belongs_to :friend,	'User', :key => true

	belongs_to :request, 'FriendshipRequest' #, :child_key => [:sender_id,:receiver_id]

	# DataMapper.auto_migrate! result:
	# CREATE TABLE "friendships" (
	#	"user_id" INTEGER NOT NULL, 
	#	"friend_id" INTEGER NOT NULL, 
	#	PRIMARY KEY("user_id", "friend_id")
	# )

end

app_models_friendship_request.rb

class FriendshipRequest
	include DataMapper::Resource

	belongs_to :sender,		'User', :key => true
	belongs_to :receiver,	'User', :key => true

	has 1, :friendship, :child_key => [:user_id,:friend_id]

end

app_models_user.rb

class User
	include DataMapper::Resource

	property :id, Serial

	has n, :friendship_requests,'FriendshipRequest', :child_key => [ :sender_id ]
	has n, :friendship_offers,	'FriendshipRequest', :child_key => [ :receiver_id ]
	has n, :friendships_requested, 'Friendship', :child_key => [:user_id]
	has n, :friendships_offered, 'Friendship', :child_key => [:friend_id]

end

application.rb

require File.expand_path('../boot', __FILE__)

# Pick the frameworks you want:
#require "active_record/railtie"
require "action_controller/railtie"
require "action_mailer/railtie"
require "active_resource/railtie"
require "sprockets/railtie"
# require "rails/test_unit/railtie"

if defined?(Bundler)
  # If you precompile assets before deploying to production, use this line
  Bundler.require(*Rails.groups(:assets => %w(development test)))
  # If you want your assets lazily compiled in production, use this line
  # Bundler.require(:default, :assets, Rails.env)
end

module Abcdefg
  class Application < Rails::Application
    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration should go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded.

    # Custom directories with classes and modules you want to be autoloadable.
    # config.autoload_paths += %W(#{config.root}/extras)

    # Only load the plugins named here, in the order given (default is alphabetical).
    # :all can be used as a placeholder for all plugins not explicitly named.
    # config.plugins = [ :exception_notification, :ssl_requirement, :all ]

    # Activate observers that should always be running.
    # config.active_record.observers = :cacher, :garbage_collector, :forum_observer

    # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
    # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
    # config.time_zone = 'Central Time (US & Canada)'

    # The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
    # config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
    # config.i18n.default_locale = :de

    # Configure the default encoding used in templates for Ruby 1.9.
    config.encoding = "utf-8"

    # Configure sensitive parameters which will be filtered from the log file.
    config.filter_parameters += [:password]

    # Enable the asset pipeline
    config.assets.enabled = true

    # Version of your assets, change this if you want to expire all your assets
    config.assets.version = '1.0'
  end
end

Gemfile

source 'http://rubygems.org'

gem 'rails', '3.1.1'

gem 'sqlite3'

DM_VERSION    = '~> 1.2.0'

gem 'dm-rails',          	DM_VERSION
gem 'dm-sqlite-adapter', 	DM_VERSION
gem 'dm-migrations',        DM_VERSION

group :development, :test do
	
	gem "rspec-rails"
	gem "rspec"
	gem "rspec-core"
	gem "rspec-expectations"
	gem "rspec-mocks"

end

spec output

rspec spec/models/friendship_spec.rb
 ~   SQL (0.048ms)  SELECT sqlite_version(*)
 ~   SQL (0.347ms)  DROP TABLE IF EXISTS "friendships"
 ~   SQL (0.037ms)  PRAGMA table_info("friendships")
 ~   SQL (31.930ms)  CREATE TABLE "friendships" ("user_id" INTEGER NOT NULL, "friend_id" INTEGER NOT NULL, PRIMARY KEY("user_id", "friend_id"))
 ~   SQL (35.497ms)  CREATE INDEX "index_friendships_user" ON "friendships" ("user_id")
 ~   SQL (4.074ms)  CREATE INDEX "index_friendships_friend" ON "friendships" ("friend_id")
 ~   SQL (0.104ms)  DROP TABLE IF EXISTS "friendship_requests"
 ~   SQL (0.027ms)  PRAGMA table_info("friendship_requests")
 ~   SQL (10.820ms)  CREATE TABLE "friendship_requests" ("sender_id" INTEGER NOT NULL, "receiver_id" INTEGER NOT NULL, PRIMARY KEY("sender_id", "receiver_id"))
 ~   SQL (2.776ms)  CREATE INDEX "index_friendship_requests_sender" ON "friendship_requests" ("sender_id")
 ~   SQL (28.672ms)  CREATE INDEX "index_friendship_requests_receiver" ON "friendship_requests" ("receiver_id")
 ~   SQL (0.107ms)  DROP TABLE IF EXISTS "users"
 ~   SQL (0.028ms)  PRAGMA table_info("users")
 ~   SQL (16.580ms)  CREATE TABLE "users" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT)

Friendship
 ~   SQL (26.612ms)  INSERT INTO "users" DEFAULT VALUES
 ~   SQL (3.146ms)  INSERT INTO "users" DEFAULT VALUES
 ~   SQL (25.233ms)  INSERT INTO "friendship_requests" ("sender_id", "receiver_id") VALUES (1, 2)
 ~   SQL (2.940ms)  INSERT INTO "friendships" ("user_id", "friend_id") VALUES (1, 2)
  should not be nil (FAILED - 1)

Failures:

  1) Friendship 
     Failure/Error: fs.request.should_not be_nil
       expected: not nil
            got: nil
     # ./spec/models/friendship_spec.rb:16:in `block (2 levels) in <top (required)>'

Finished in 5.92 seconds
1 example, 1 failure

Failed examples:

rspec ./spec/models/friendship_spec.rb:7 # Friendship 

spec_models_friendship_spec.rb

describe Friendship do

	before(:all) do
		DataMapper::Model.raise_on_save_failure = true
	end
	
	it do
		user = User.create
		friend = User.create
		req = FriendshipRequest.create(:sender => user, :receiver => friend)
		fs = Friendship.create(:user => user, :friend => friend, :request => req)
		
		fs.request.should == req
		fs.reload
		# Since the request-property is not present in the DB, it is set to nil
		fs.request.should_not be_nil
	end
end

spec_spec_helper.rb

ENV["RAILS_ENV"] ||= 'test'
require File.expand_path("../../config/environment", __FILE__)
require 'rspec/rails'

Dir[Rails.root.join("spec/support/**/*.rb")].each {|f| require f}

RSpec.configure do |config|
	config.before(:suite) do
		logger = DataMapper::Logger.new(STDOUT, :debug)
		DataMapper.auto_migrate!
	end
end