gistfile1.rb

module War
  class War::Character
    include DataMapper::Resource

    property :id, Serial
    # ...

    has n, :raid_participations, :class_name => 'War::RaidParticipants'
    has n, :raids, :class_name => 'War::Raid', :through => :raid_participations, :child_key => [:character_id]

    before :destroy do
      raid_participations.destroy!
    end
  end

  class Raid
    include DataMapper::Resource

    property :id, Serial
    # ...

    has n, :raid_participants, :class_name => 'War::RaidParticipants'
    #FIXME: see hack below

    #FIXME: HACK alert
    # this is a workaround for broken m:n associations
    def characters
      @characters || @characters = raid_participants.character
    end

    def remove_characters(cs)
      unless cs.empty?
        raid_participants.all(:character_id => cs.collect {|c| c.id}).destroy!
      end

      @characters = raid_participants.character
    end

    before :save do
      characters unless @characters
      cs = raid_participants.character

      cs.each do |c|
        c.destroy unless c.in? @characters
      end

      @characters.each do |c|
        raid_participants.new(:character_id => c.id) unless c.in? cs
      end
    end

    before :destroy do
      raid_participants.destroy!
    end
  end

  class RaidParticipants
    include DataMapper::Resource

    property :raid_id, Integer, :key => true
    property :character_id, Integer, :key => true

    belongs_to :raid, :class_name => 'War::Raid', :child_key => [:raid_id]
    belongs_to :character, :class_name => 'War::Character', :child_key => [:character_id]
  end
end