CRUD pattern for has_many relationships (forms containing co

Hello folks!

Beare with me for a second, while I explain my problem.

Assuming we have the trivial model of

class Author
has_many :books

class Book

How do people go about creating the authors/edit and authors/new
views if you want to be able to add and remove arbitrary amount of
Books at Author creation and edit time? What I mean by this is that I
go to ‘authors/new’ then add a few Books and then create the Author.

Let’s assume that I am using link_to_remote for the on the fly
addition of Books to the Author. It is important that neither the
Author nor the Books are saved to the database until the Create form
button is pressed.

My solution so far is to use the session object to keep an Array with
new Books that are not saved in the database.

I have a books/_book.rhtml partial

<p><%= text_field_tag "books[#{}][title]", book.title %></p>

…an authors/_form.rhtml partial

<%= text_field "author", "name" %>
<%= link_to_remote "Add book", :url => {:action => "add_book"}
							    :update => "books_list" %>

<div id="books_list">
	<%= render :partial => "books/book", :collection => author.books %>

…and in authors_controller.rb

def new
	session[:books] =

def add_book
	book = => "untitled") = -session[:books].size
	session[:books] << book
	render :partial => "books/book", :collection => session[:books]

def create
  # code ommited but..
 # I look for session[:books] and iterate through each adding a new

one if it has a
# negative id, otherwise find the exisiting book (when coming from
an edit)

The above approach breaks down when adding books because is
not defined yet. The ugly hack is that I am setting the id to a
negative value so that I can then spot it in my create method and
create proper Book objects. The above works for the edit mode.

This gets even messier if you have Chapters and a Book has_many
chapters. There seems to be no recursive way of creating and then
parsing all these.


Hmmm. Well I’m sure exactly what your problem is, and I don’t know how
attached you are to your links approach to adding books, but this is the
checkbox form I have for a similar structure:

(listings habtm categories)

<% for category in @categories %>

checked="checked"<% end %> > <%= h( %>
<% end %>

Then in the create code I have:

@listing.categories = Category.find(params[:category_ids])

The same can work for a book with chapters. I hope this helps.


That first line should read, “I’m NOT sure exactly what your problem
is…” >_>

Hello Adam.

Maybe I didn’t explain my problem very well.

I know how to add EXISTING books to a new author at creation time,
like you showed below.

What I need though is to be able to create one or more NEW books when
creating a new Author. The books can have more than just one
attribute (e.g. name, isbn, num_of_pages). And I need to do it
inline in my Author form.