ActiveResource and a philosophical REST question

For all the REST fans out there, I have two questions.

Usually when we think of RESTful urls, we think in terms of rather
simple struct-like objects. The canonical example is using
ActiveResource to create person objects:

POST /people


We expect to get back a 201 response with the url to the newly-created
resource, like /people/47. If I GET /people/47, I should see the
exact same data as when I created it.

My first question is, what if this is not a symmetrical operation?
For example, let’s say I want to transmit a pizza order:

POST /orders


Here I’m ordering combo #3, which is a actually a large pepperoni, a 6-
pack of root beer, and a slice of tiramisu. The server responds with
a 201 to /orders/342.

But if I do a GET /orders/342, I might see this:

342 Jeff 555-555-1212 1 18" Pepperoni 1 2 Root Beer 6 1 Tiramisu 1

Is this kind of thing acceptable in the REST world? I hope so,
because having the client create each step of the hierarchy would be a
pain (first create an empty order, then create each line item, etc.)

My second question is, how would I create the pizza order using
ActiveResource? In other words, do I need to worry that the
attributes that I use for the create action are not the same as the
attributes I’ll be receiving?


On 9/27/07, Jeff [email protected] wrote:


Thanks! Jeff

Of course it’s acceptable. There’s nothing that says that the client
needs to send a hash to the server and the server needs to persist it,
and that’s all you can do.

Think about what you’re trying to do. You’re creating a new order
resource. What info does it take to do that? Apparently in your case
sending a combo ID is sufficient. The server can handle it however
you want.

As far as how you create it, I think you just showed us. You pass
some info into the controller. This might lead to something like:

class Order < ActiveRecord::Base

def combo=(cid)
c = Combo.find cid
c.items.each {|i| items << i }

or however you choose to implement it.


Jeff, don’t forget that the server responds to the POST to /orders with
created’ in the Status header and the URL ‘/orders/342’ in the
header (!).The actuall content being returned by the POST request is

342 Jeff 555-555-1212 1 18" Pepperoni 1 2 Root Beer 6 1 Tiramisu 1

Instead of the POST’ed parameters and is actually the same content as is
retreived by ‘GET /orders/342’.

I hope this clears things up a bit for you.

  • Matthijs

On Sep 28, 2:20 am, “Matthijs L.” [email protected]


Some implementations just do a HEAD on the created resource, but
you’re right that the full xml can be returned as well.


On Sep 28, 12:32 am, “Pat M.” [email protected] wrote:

or however you choose to implement it.


Sorry, I meant what does the client side (the code that’s using
ActiveResource) look like; or more specifically, will I run into any
trouble using ActiveResource to create the order and to retrieve the
order, when the parameters are different going and coming (i.e. if
ARes is doing any sort of parameter caching, and will I be confusing
that caching).