Question

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)?

Answer 1

No, as there is virtually no use-case for this. If your record cannot exist without an associated record, you should probably be preventing the record from being saved, not shoe-horning in some kind of pseudo-null object to take its place.

The closest approximation would be a before_save callback:

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

  before_save :create_default_price

  def create_default_price
    self.price ||= create_price
  end

end