Creating form for associated has_many model

Rails
1

This example shows how to create a form for an associated model
‘Comment’, where ‘Comment’ belongs_to ‘Post’ and 'Post has_many
‘Comments’.

How might I modify that to display all the comments in the form, and
still have it call the CommentsController (versus having the form call
the PostsController, as in the example here
#17 HABTM Checkboxes - RailsCasts)?

Thanks

2

To ask another way:

Using a Polymorphic Assocation, if Photo and Article each ‘has_many’
Comments, the comment form should call the CommentsController, as
shown here #154 Polymorphic Association - RailsCasts
– But what if I’m editing multiple comments in one form for a given
Photo. In this case should the form still call the CommentsController
or is it better off calling the PhotoController?