gistfile1.rb

require "rubygems"
require "dm-core"

class Word
  include DataMapper::Resource

  property :id,       Serial
  property :text,     String

  has n, :translations #, :model => 'Word', :foreign_key => [:word_id]
  has n, :words, :through => :translations, :foreign_key => [:word_id]
end

class Translation
  include DataMapper::Resource

  property :word_id, Integer, :key => true
  property :translation_id, Integer, :key => true

  belongs_to :word,        :model => 'Word', :child_key => [:word_id]
  belongs_to :translation, :model => 'Word', :child_key => [:translation_id]
end


DataMapper.setup(:default, 'sqlite3::memory:')
Word.auto_migrate!
Translation.auto_migrate!

t = Translation.create :word => Word.create(:text => 'y'), :translation => Word.create(:text => 'x')
puts t.inspect

puts Word.first.translations.inspect