has_n_through_resource.rb

require 'rubygems'
require 'dm-core'

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

class Quote
  include DataMapper::Resource
  property :id,         Serial
  has 0..n, :billings, :through => Resource
end
 
class Billing
  include DataMapper::Resource
  property :id,         Serial
  
  has 0..n, :quotes, :through => Resource
end

puts DataMapper::Model.descendants.inspect

DataMapper.auto_migrate!

puts DataMapper::Model.descendants.inspect

__END__

[ree-1.8.7-2009.10] mungo:extlib snusnu$ ruby foo.rb 
#<DataMapper::Model::DescendantSet:0x10165a778 @ancestors=nil, @descendants=[Quote, Billing]>
 ~ (0.000038) SELECT sqlite_version(*)
 ~ (0.002727) DROP TABLE IF EXISTS "quotes"
 ~ (0.002216) DROP TABLE IF EXISTS "billings"
 ~ (0.002530) DROP TABLE IF EXISTS "billing_quotes"
 ~ (0.000024) PRAGMA table_info("quotes")
 ~ (0.002243) CREATE TABLE "quotes" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT)
 ~ (0.000047) PRAGMA table_info("billings")
 ~ (0.004413) CREATE TABLE "billings" ("id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT)
 ~ (0.000022) PRAGMA table_info("billing_quotes")
 ~ (0.002807) CREATE TABLE "billing_quotes" ("quote_id" INTEGER NOT NULL, "billing_id" INTEGER NOT NULL, PRIMARY KEY("quote_id", "billing_id"))
#<DataMapper::Model::DescendantSet:0x10165a778 @ancestors=nil, @descendants=[Quote, Billing, BillingQuote]>