gistfile1.rb

class Game
  include DataMapper::Resource
  
  #
  # Properties
  #
  property :id, Serial
  
  #
  # Associations
  #
  has n, :game_memberships
  has n, :players, :through => :game_memberships

end

class CaptainGame < Game

  has n, :captain_memberships, 'GameMembership', :child_key => [ :game_id ], :captain => true
  has 2, :captains,            :through => :captain_memberships, :via => :players

end

class GameMembership
  include DataMapper::Resource
  
  #
  # Properties
  #
  property :id,      Serial
  property :captain, Boolean, :nullable => false, :default => false

  # 
  # Associations
  #
  belongs_to :game
  belongs_to :player

end

class Player
  include DataMapper::Resource
  #
  # Properties
  #
  property :id,     Serial

  # 
  # Associations
  #
  has n, :game_memberships
  has n, :games, :through => :game_memberships

end

DataMapper.setup(:default, 'sqlite3::memory:')
DataMapper.auto_migrate!
require 'dm-sweatshop'
Player.fix {{ }}
Game.fix {{ }}
require 'bacon'

describe 'CaptainGame' do
  it 'should assign 2 captains' do
    players = 5.of {Player.gen}
    game = CaptainGame.gen(:captains => players[0..1])
    game.captains.should.equal players[0..1]
    game.players.should.equal players[0..1]
    game.players << players[2..4]
    game.captains.should.equal players[0..1]
    game.players.should.equal players
  end
end