Rails - Sep 2006 - possible to create polymorphic relationship with STI models?

I would like to associate a ‘product’ model with 3 models inherited from 
‘image’: part, action and accessory.

I have it working with Has_many :through relating products to images 
through attachments, I then have to determine the ‘type’ of the STI 
extension. This means i have to go product.images. While this is ok, i 
can see it getting tricky when i want to go products.images << 
Part.create(:name => "test"). (im on edge rails so the << 
should work)

I would like to have the parts, actions or accessories collections 
available under products eg products.parts.

I have the following tables: product - attachment - images, each with 
their own model.
I also have 3 models that inherit from image eg Part < Image.

Ive been following the hasmanythrough article ''the other side of 
polymorphic''. As well as read most of the other articles...but i just 
dont get how this will work.

According to the docs has_many ignores class_name when using :through. 
"Options for :class_name and :foreign_key are ignored, as the 
association uses the source reflection."

   1. Attachment tables:
   2.
   3. (polymorphic attempt)
   4. create_table "attachments", :force => true do |t|
   5. t.column "product_id", :integer
   6. t.column "attachable_id", :integer
   7. t.column "attachable_type", :string
   8. t.column "created_at", :datetime
   9. t.column "created_by", :integer
  10. end
  11.

  20.
  21. Models:
  22. class Product < ActiveRecord::Base
  23. has_many :parts, :through => :attachments,
  24. :class_name => :parts,
  25. :conditions => "attachments.attachable_type =
''Image''"
  26. end
  27.
  28.
  29. class Attachment < ActiveRecord::Base
  30.
  31. belongs_to :product
  32. belongs_to :attachable, :polymorphic => true
  33.
  34. belongs_to :part, :class_name => "Part",
  35. :source => :image,
  36. :foreign_key => "attachable_id"
  37. end
  38.
  39. class Part < Image
  40. has_many :attachments, :as => :attachable
  41. has_many :products, :through => :attachments
  42. end


Through the console i can do the following:

   1. Part.find(:first).products.count
   2. >> 1


But this fails

   1. Product.find(:first).parts
   2. >> ActiveRecordHasManyThroughSourceAssociationNotFOundError
   3. ..
   4. ..
   5. ..
   6. associations.rb:876: in ''parts''


This is what i need to work and it doesnt. The many models are the ones 
that can access the shared models..but not the reverse..hmmm. Thats a 
pain if your shared model

Also, i still have no idea how to create the association with 
polymorphism. Its easy with just :through ! Im going to go back to the 
:through association as it makes more sense to me.

Would love to hear that im really close and just need to change x and 
y... =)

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As an update:
With the assistance of the new features of edge rails i ahve been able 
to do the follwoing, brilliant !

product = Product.find(:first)
product.images << Part.create(:name => "test part")

Remembering that part is a STI instance of image.


Which means the only thing i really need to do now is create a way to 
get the parts, accessories or actions associated with a product. 
Enabling the following to work:

product.parts (returns parts from images table)

i have an idea that it should be some sort of association extension in 
the products model..just not sure how to do it. Any ideas ?

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GOT IT !!

it was just this... finally !

class Product < ActiveRecord::Base

  # through
  #products - attachments - images
  has_many :attachments

  has_many :parts,        :through => :attachments,
                          :source => :image,
                          :conditions => "images.type
=''Part''"

  has_many :accessories,  :through => :attachments,
                          :source => :image,
                          :conditions => "images.type
=''Accessory''"

  has_many :actions,      :through => :attachments,
                          :source => :image,
                          :conditions => "images.type
=''Action''"

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