Nested model form


I’ve got a problem with nested model form. I need to post just
Comments. And they are referenced to Links which are referenced to

The current form in app/views/links/show.html.erb doesn’t work for me.
I want it to be able to post new comment to links. In the Links
controller I’ve got:
@link = Link.find(params[:id])
form_for @link, If there were no Categories but
how it would look in the current structure ?

Best Regards