As we all know, the Rathole plugin was sucked into Rails core with the release of Rails 2 and now using fixtures has become, um, foxier.  One use case that wasn't immediately clear to me was how to specify polymorphic relationships using the new and improved syntax.  It turns out that this is straightforward.

Let's say your application captures contact information for several models.  Our hypothetical application is a brand new social network for people in the music industry.  (Quick, let's pitch it to VCs!)  Each application user would have contact information and, since they are in the music industry, they belong to a Record Label.  Record Labels also have contact information stored for them.  So we get this:

 1  class Contact < ActiveRecord::Base
 2    belongs_to :contactable, :polymorphic => true
 3  end
 4    
 5  class User < ActiveRecord::Base
 6    has_one :contact, :as => :contactable
 7  end
 8  
 9  class Label < ActiveRecord::Base
10    has_one :contact, :as => :contactable
11  end

Now to set up the fixtures.  All you need to do is specify the contactable name and contactable_type for each contact and we are done.

 1  # User
 2  music_industry_person:
 3    username: person1
 4    password: secret
 5    
 6  # Label
 7  label1:
 8    name = Some Indie Label
 9    
10  # Contact
11  fred:
12    contactable: music_industry_person
13    contactable_type: User
14    first_name: Fred
15  
16  sam:
17    contactable: label1
18    contactable_type: Label
19    first_name: Sam

As you can see, a piece of cake!

Update:  Phil knew a one liner way to do this:

1  sam:
2    contactable: label1 (Label)
3    first_name: Sam