Re: Modeling conditional update based on existence of a dependent resource

On Tue, Jul 3, 2012 at 12:33 PM, Shaunak Kashyap <[email protected]>wrote:

> **
>
>
> Hi folks,
>
> I am looking to model an interaction in my REST application where the
> client should only be allowed to modify a resource (say "B") if another
> resource (say "A") exists.
>
> Using HTTP, if resource A exists, I would like PUT /uri/for/resource/B to
> succeed. If resource B does not exist, I would like the same PUT request to
> fail, responding with a status code that indicates to the client that
> resource A does not exist. So what is a good status code to respond with in
> the failure case? I considered 403 Forbidden but its semantics say that
> "the request should not be repeated". This does not quite make sense in my
> application since resource A might come into existence in the future,
> making it okay for the client to re-issue the same PUT request for resource
> B.
>

Would 404 not suffice here?


>
> Alternatively (or additionally?), perhaps the client could issue a
> conditional PUT on resource B which would only succeed if resource A
> existed. How could I express such a condition in HTTP? I considered using
> the If-Match request header but that seems to apply to representations of
> the same resource (in my example, B) rather than of other resources (in my
> example, A).
>

You could use a Link header in the error response that has a relation type
called something like "depends-on-existence", and point that link to
resource A.

Cheers,
M