Two apps, both running Rails 2.3.2, local machine, development
environment, just to clarify that all gems are the same (obviously)
and most of the code is “standard fare” — CRUD and such, nothing
fancy going on.
Now that that’s out of the way, here’s the issue…
In both apps, I have objects which “belong_to” another object, of
which both have accepts_nested_attributes_for said objects.
In both apps, in the form view for each particular object, I want to
do multiple-child-object creation… So in other words, in App 1, I
have loan_applications. loan_application has_many :items – as such,
an item belongs_to :loan_application
Thus I am able to generate 3 sets of “item fields” in the form so that
a user can essentially create 3 items along with their application.
In App 2, I have products. Similarly, product has_many :photos, :as
=> :owner, and therefore photo belongs_to :owner, :polymorphic =>
true.
So, as you can see the only difference so far is the polymorphism.
However, a photo also has_attachment, since I am using attachment_fu.
I am re-using the code that I wrote for the loan_application items for
the product photos. Fairly straightforward, right? Very similar
assocation (just has_many on both)… but the form output is
completely different. The photos don’t output the proper id or name
attributes on the file field. Take a look at the pastie below, you
will see very very few differences between the two (in fact they are
differences I already pointed out, polymorphism and attachment_fu).
So my thought is, maybe nested fields_for hasn’t come far enough for
polymorphic associations? That just seems quite odd…
Any thoughts/feedback/musings welcome, I’d love to get this figured
out so that I can continue on to bigger-better problem-solving 
Cheers!