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

class Event < ActiveRecord::Base
  has_one :address, :as => :addressable, :dependent => :delete
end

class Contact < ActiveRecord::Base
  has_one :address, :as => :addressable, :dependent => :delete
end


# app/views/events/edit.html.haml
- form_for :event do |f|
  %p= f.text_field :name
 
  - f.fields_for :address do |a|
    %p= a.text_field :street
    # ...