Wong likes pie

gistfile1.rb

def price
  return @price if @price
  @price = Money.new(self.cents || 0, self.some_relationship.currency || Money.default_currency)  
end

def price=(new_price)
  @price = new_price.to_money
  self.cents = @price.cents
  self.some_relationship.currency = @price.currency_as_string
end

before_save save_relationship_if_currency_changed
def save_relationship_if_currency_changed
  self.some_relationship.save if self.some_relationship.currency_changed?
end

#beware that saving this model can save the other one, just in case you don't intend to save it