Rails 3 create form for Polymorphic Association's child model

My application's route.rb file contains this namespace:

 namespace :admin do
       resources :index
       resources :posts do
           resources :images
         end
       resources :statics
     end

I used Polymorphic Association

Post model: has_many :images, :as => :imageable

Image model: belongs_to :imageable, :polymorphic => true

And I created necessary fields in migration.

When I call @post.images,开发者_JS百科 no error message, I think this relation works fine.

I think, my problem is in the image uploader form, I use code like this: (post/edit action)

[there is post edit form]
<% form_tag admin_post_images_url( @post ) , :multipart => true do %>
    <%= file_field  :imageable, :photo, :size => 40 %>
    <input type="submit" name="send" value="upload!" />
<% end %> 

The image is successful uploaded, but imageadble_id and _type doesnt filled. Something wrong (I think with admin_post_images_url( @post ) part), what is the problem?

update:

When I add manual to create imageadble_id and type, and listing its work, so assotiation is works good.

Try something like this:

<% form_for([:admin, @post, @image], :multipart => true) do %>

This may not work exactly but should get you started down the right path. No matter what, you need "form_for" if you're working with a model, not "form_tag".