gistfile1.rb

class Person
  include MongoMapper::Document
end

class Registree < Person
  key :in_wels,   Boolean
  key :in_vienna, Boolean
end

class Visitor < Registree
  # QUERY = { "$or" => [{:in_wels => true}, {:in_vienna => true}] }

  def self.query(options={})
    super.tap do |query|
      query["$or"] = [{:in_wels => true}, {:in_vienna => true}]
    end
  end
  
  def self.name
    "Registree"
  end
end