gistfile1.rb

#!/usr/bin/env ruby

require 'dm-core'
require 'dm-sweatshop'

class Foo
  include DataMapper::Resource
  property :id, Serial

  has n, :bars
  belongs_to :current_bar, :model => 'Bar', :child_key => [:current_bar_id], :nullable => true
end

class Bar
  include DataMapper::Resource
  property :id, Serial

  belongs_to :foo, :nullable => true
  has n, :bazs
end

class Baz
  include DataMapper::Resource
  property :id, Serial

  belongs_to :bar
end

Foo.fix {{
  :bars => (1..3).of { Bar.make }
}}

Bar.fix {{
  :foo => Foo.make,
  :bazs => (1..3).of { Baz.make }
}}

Baz.fix {{
  :bar => Bar.make,
}}

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

foo = Foo.gen
foo.update(:current_bar => foo.bars.first)