REST help

Hi all,

I am trying to build a RESTful shopping cart and I have hit a small
wall, but before I get to that let me explain what I have done thus far.

I have two RESTful controllers, CartController and CartItemsController
with a nested routes setup like so

map.resources :carts do |carts|
carts.resources :cart_items, :collection => {:empty => :delete}

(I added a custom route to the for emptying the cart as it seemed to me
that when I clear the cart I am operating on the items which is why I
added that action to the CartItemsController. If this is not RESTfully
“correct” I would love to hear about it!)

Using the nested routes I am using the CartItemsController to perform
the CRUD operations on CartItems and assigning them to the proper cart
(e.g. adding an item would link to POST /carts/1/cart_items). When a
user attempts to add an item to the cart that is already there, from
what I understand of REST, this should be an update (i.e. PUT
/cart/1/cart_items/23) with the new attributes for the item. All I
should have to do is change the submission form where the user is doing
the update from a POST to a PUT depending on whether the item they are
about to add is in the cart already.

BUT, what if I am using AJAX to update the cart? When the form is
initally generated it will use a create action. When the user adds the
item to cart, the page does not refresh and the form retains it create
action. If the user uses the form again the item will become a new line
item in the cart. Do you see where I am going with this?

Possible solutions I have kicked around is doing a check in the
CartItemsController create action to see if the item is already in the
cart and the update it, but that seems just plain wrong. Using RJS
updating to update the form with a new URL and additional field with the
CartItem ID or creating a custom action to handle all of this (seems
wrong too!)

I am really starting to enjoy using RESTful development, but I think I
just know enough to be dangerous so if anyone could give me some advice
on the more ‘correct’ way to solve this problem that would be fantastic.
Also, if anyone knows of really good resource about resources (like how
to identify) please pass it along.