hstore_accessor.rb

# include from an initializer

module HstoreAccessor
  def hstore_accessor(hstore_attribute, *keys)
    Array(keys).flatten.each do |key|
      define_method("#{key}=") do |value|
        send("#{hstore_attribute}_will_change!")
        send("#{hstore_attribute}=", (send(hstore_attribute) || {}).merge(key.to_s => value))
      end
      define_method(key) do
        send(hstore_attribute) && send(hstore_attribute)[key.to_s]
      end
    end
  end
end

ActiveRecord::Base.send(:extend, HstoreAccessor)