sti.rb

require 'rubygems'
require 'dm-core'

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

class GameConsole
  include DataMapper::Resource
  property :id, Serial
  property :type, Discriminator

  def producer
    "invalid"
  end
end

class Wii < GameConsole
  def producer
    "Nintendo"
  end

end

class XBox < GameConsole
  property :xbox_live, Boolean

  def producer
    "Microsoft #{xbox_live}"
  end
end

DataMapper.auto_migrate!

XBox.create(:xbox_live => true)
Wii.create

# The next line causes the following error:
# /usr/local/lib/ruby/gems/1.8/gems/dm-core-0.10.2/lib/dm-core/query.rb:803:in `assert_valid_fields': +options[:field]+  entry :xbox_live does not map to a property in GameConsole (ArgumentError)


GameConsole.all.map {|gc| gc.producer}