Understanding Rails Controllers/Models

Hello, Rails newbie... trying to understand the right way to do

In my app users can create a Book ( I have that working)

What I want to happen is when a user creates a book, a record is added
to the BookCharacters Table, something like (id, book.id, user.id,

When the book is created, the user who created it should automatically
be added as the first BookCharacter. After than the user can then
manually add/edit as many BookCharacters as they want. But initially I
want them added automatically by default.

So in my Book controller I have:
def create
@book = Book.new(params[:book])
respond_to do |format|
  if @book.save

With Rails, is it the practice to add that kind of logic after the
book is saved? Something like
Book.create( :creator => current_user.id)


Forgot to add. I'm using Rails 3. thxs