standalone_example.rb

#!/usr/bin/env ruby -Ku

# encoding: utf-8

require 'rubygems'
require 'dm-core'

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'sqlite3::memory:')

class Person
  include DataMapper::Resource

  property :id, Serial

  has n, :mailer_people
  has n, :conversations, 'Mailer', :through => :mailer_people, :via => :mailer
end

class MailerPerson
  include DataMapper::Resource

  property :person_id, Integer, :min => 1, :key => true
  property :mailer_id, Integer, :min => 1, :key => true

  belongs_to :person
  belongs_to :mailer
end

class Mailer
  include DataMapper::Resource

  property :id, Serial

  has n, :mailer_people
  has n, :people, :through => :mailer_people
end

DataMapper.auto_migrate!

puts '-' * 80, 'Create Mailer, then Person, then intermediary'
Mailer.create(:people => [ {} ])

puts '-' * 80, 'Create Person, then Mailer, then intermediary'
Person.create(:conversations => [ {} ])