Rails 2.3 Updating multiple objects at once

Question

I have a small app that has an edit form with multiple rows in a form. I followed the advice in the rails way book, page 364-365 and it worked perfectly. I am trying to update the app to run in 2.3 and the method described is now broken.

The models are Course has many Books Book has many Courses Order belongs to course, books

The controller gets a list of books to edit and is named @books. In the view I have:

<% form_for 'book[]', :url=>{:action=>'edit_order',:id=>@course} do |form| %> <% for @book in @books %> ...

The error I get is: object[] naming but object param and @object var don't exist or don't respond to to_param: nil

If the form would display and get submitted the controller has this to update the records:

Book.update(params[:book].keys, params[:book].values)

What do I need to change to get this working again?