composite keys and association

i have two table, comment and post, both have composite keys, and no id
column, comment belongs to post, i follow the instruction of, and it seems successfully,
(But i still cant confirm to put require 'rubygems' and
require 'composite_primary_keys' on which file ).
I can do the CRUD operation for post,then i want to create comment form,
in the _form.html.erb, the code likes below:
<%= form_for([@post,]) do |f| %>
then i got an error,"unknown attribute: comment_id",
i think the build method need the parameter id which is default, but i
dont have this column,and i cant change any thing in the database,how to
resolve this problem?Thanks .

A way to resolve the problem is to stick to the rails conventions for
id columns and so on. That is the best way unless you have a legacy
database and *really* cannot change the schema.


Colin Law wrote in post #1039519:

In that case some of the clever stuff in Rails may not be available to
you, you may have to do them 'by hand' so to speak. I don't know
whether there is a way of using build in the way you want in your
circumstance. The alternative is just to create the object
explicitly. I expect you have already googled for
rails legacy database
to get as far as you have.