test case for apparent bug regarding association inheritance

.gitignore

Gemfile.lock

dm_assoc.rb

#!/usr/bin/env ruby
# encoding: UTF-8

# test case for apparent bug regarding association inheritance

require "rubygems"
require "dm-core"
require "dm-constraints"
require "dm-migrations"

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/db.sqlite")

# models

class Company
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :required => true

  has n, :vehicles, :constraint => :destroy

end

class LicensePlate
  include DataMapper::Resource

  property :id, Serial
  property :registration, String, :required => true

end

class Vehicle
  include DataMapper::Resource

  property :id, Serial
  property :type, Discriminator
  property :name, String, :required => true

  belongs_to :company

end

class Car < Vehicle

  # `required => false` avoids FK property with a not-null constraint, which
  # would prevent saving higher-level models
  belongs_to :license_plate, :required => false

end

DataMapper.finalize
DataMapper.auto_migrate!

# generate data

Car.create :name => "KITT",
    :company => Company.create(:name => "Knight Industries"),
    :license_plate => LicensePlate.create(:registration => "KNIGHT")

# retrieve data

puts "\n[INFO] retrieving license plate via direct association"
puts "[INFO] ... via superclass"
p Vehicle.first                  # #<Car @id=1 @type=Car @name="KITT" @company_id=1 @license_plate_id=<not loaded>>
p Vehicle.first.license_plate    # #<LicensePlate @id=1 @registration="KNIGHT">
puts "[INFO] ... via class"
p Car.first                      # #<Car @id=1 @type=Car @name="KITT" @company_id=1 @license_plate_id=1>
p Car.first.license_plate        # #<LicensePlate @id=1 @registration="KNIGHT">

puts "\n[INFO] retrieving license plate via indirect association"
Company.first.vehicles.each do |vehicle|
  p vehicle                      # #<Car @id=1 @type=Car @name="KITT" @company_id=1 @license_plate_id=<not loaded>>
  p vehicle.license_plate        # nil
  puts "[ERROR] failed to retrieve license plate" if vehicle.license_plate.nil?
end

Gemfile

source :rubygems

DM_VERSION = "1.2.0"

gem "dm-core", DM_VERSION
gem "dm-constraints", DM_VERSION
gem "dm-migrations", DM_VERSION
gem "dm-sqlite-adapter", DM_VERSION