Is there a DSL for creating an object in an AR relationship that would be the opposite of `:dependent => destroy` (in other words create an object so that it always exists). Say, for example, I have the following:

```
class Item < ActiveRecord::Base
  #price
  has_one :price, :as => :pricable, :dependent => :destroy
  accepts_nested_attributes_for :price
  ....

class Price < ActiveRecord::Base
    belongs_to :pricable, :polymorphic => true
    attr_accessible :price, :price_comment

```

I'm thinking I'd like for a price to be created every time even if we don't specify a price? Is the only (or best) option to do this as a callback or is there a way to do this via a DSL (similar to `:denpendent => :destroy`)?