Gist showing nested/self-referential model

folder.rb

class Folder
  include DataMapper::Resource
  
  has n, :subfolders, 'Folder'
  has n, :messages
  belongs_to :parent, :model => 'Folder', :required => false
  belongs_to :owner, :model => 'User', :key => true
  
  property :id, String, :key => true
  property :name, String
  property :special, String
end

script.rb

#!/usr/bin/env ruby
#
# Not quite as elegant, but brute force seems to work.
require 'rubygems'
require 'dm-core'
require 'dm-migrations'


# setup the logger
DataMapper::Logger.new($stdout, :debug)

# connect to the DB
DataMapper.setup(:default, 'sqlite3::memory:')

class User
  include DataMapper::Resource

  has n, :folders, :child_key => [:owner_address]

  property :address, String, :key => true, :required => true
  property :name, String
end

class Folder
  include DataMapper::Resource

  property :id, String, :key => true
  property :name, String
  property :special, String
  property :owner_address, String, :key => true, :required => true

  has n, :subfolders, 'Folder', :child_key => [:parent_id, :owner_address]
  belongs_to :parent, 'Folder', :required => false, :child_key => [:parent_id, :owner_address]
  belongs_to :owner,  'User',   :key => true, :child_key => [:owner_address]

end

DataMapper.finalize.auto_migrate!

u = User.create(:address => 'a@b.c')
f = Folder.create(:id => 'test', :owner => u)
sf = Folder.create(:id => 'example', :owner => u, :parent => f)

__END__


 ~ (0.000102) SELECT sqlite_version(*)
 ~ (0.000234) DROP TABLE IF EXISTS "users"
 ~ (0.000053) PRAGMA table_info("users")
 ~ (0.000435) CREATE TABLE "users" ("address" VARCHAR(50) NOT NULL, "name" VARCHAR(50), PRIMARY KEY("address"))
 ~ (0.000076) DROP TABLE IF EXISTS "folders"
 ~ (0.000041) PRAGMA table_info("folders")
 ~ (0.000309) CREATE TABLE "folders" ("id" VARCHAR(50) NOT NULL, "name" VARCHAR(50), "special" VARCHAR(50), "owner_address" VARCHAR(50) NOT NULL, "parent_id" VARCHAR(50), PRIMARY KEY("id", "owner_address"))
 ~ (0.000127) CREATE INDEX "index_folders_parent" ON "folders" ("parent_id")
 ~ (0.000102) INSERT INTO "users" ("address") VALUES ('a@b.c')
 ~ (0.000119) INSERT INTO "folders" ("id", "owner_address") VALUES ('test', 'a@b.c')
 ~ (0.000125) INSERT INTO "folders" ("id", "owner_address", "parent_id") VALUES ('example', 'a@b.c', 'test')

user.rb

class User
  include DataMapper::Resource
  
  belongs_to :domain
  
  has n, :folders
  has n, :messages, :through => :folders
  
  property :address, String, :key => true, :required => true
  property :password, BCryptHash, :required => true
  property :name, String
end