polymorphic_candidate.rb

class Address < ActiveRecord::Base

  DELTA = 0.001

  validates :line1, :city, :presence => true
  belongs_to :country
  belongs_to :organisation
  belongs_to :person
  belongs_to :address_type
  belongs_to :service

# more code

end

class Address < ActiveRecord::Base
   belongs_to :addressable, :polymorphic => true

end

class Organization < ActiveRecord::Base
  has_many :addresses, :as => :addressable

# ...

end

using_active_record_methods.rb

class Organisation < ActiveRecord::Base 

 def registered_address
   self.addresses.each do |addr|
      if addr.address_type_id == 1
        return addr
      end
    end
    nil
  end

# could be written simply
 def registered_address
  addresses.where(:address_type_id => 1).first
 end
end

  def find_phone(phone_number, phone_type_id)
    phones.where(:number => phone_number, :phone_type_id => phone_type_id).first
    # self.phones.each do |phone|
    #   if phone.number == phone_number and phone.phone_type_id == phone_type_id
    #     return phone
    #   end
    # end
    # nil
  end