Set a select box with default value selected

I am relating to the book & subject example mentioned in the tutorial
mentioned here:

There is a file that goes like show_subjects.html.erb and it will list
all the books for that particular subject we've selected.

Suppose if there were no books to show for the subject we can ideally
show a corresponding message like "there are no books for this subject

I'd like to rewrite that is "there are no books for this subject,
would you like to add one?"

Lets say that the 'would you like to add' part is a link to the book
create view where in we add a book. How do I load that page to have
its select box show the subject tht had no books (from where I was
initially at)...?


Something like...

# views/subject/show
  <%= link_to 'Would you like to add one?', new_book_path, {:subj => @subject} %>

# controllers/books_controller
  def new
    @book =
    @book.subject = params[:subj]
    # etc...



How do I re-write the new.html.erb?