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# app/models/wizard.rb
class Wizard
  # shared instance methods go here

  def self.all_visible_subwizards
    descendants.entries.select{|d| d.visible?}.sort
  end
end

# lib/wizard_fields.rb
module WizardFields
  def self.included(base)
    base.class_eval do
      property :id,    DataMapper::Property::Serial
      property :state, String
    end
  end
end

# app/models/foo_wizard.rb
class FooWizard < Wizard
  include DataMapper::Resource
  include WizardFields
  # some associations here

  class << self
    def description
      "foo wizard"
    end

    def visible?
      true
    end
  end

  # state machine logic down here, other methods
end

# app/models/bar_wizard.rb
class BarWizard < Wizard
  include DataMapper::Resource
  include WizardFields
  # some associations here

  class << self
    def description
      "bar wizard"
    end

    def visible?
      true
    end
  end

  # state machine logic down here, other methods
end