Code review comment for lp:~leonardr/lazr.restful/version-specific-request-interface

This branch changes the way an incoming web service request is associated with a specific version of the web service. Previously, the version number was stuffed into a Zope annotation on the request object. Versioned lookups were done as named lookups using the version number as the name.

Now, the web service is expected to define a marker interface for every version it publishes, eg. IWebServiceRequestBeta. Once the traversal code knows which version of the web service the client is requesting, it calls alsoProvides on the request object to mark it with the appropriate marker interface.

The idea here is to get rid of named lookups. Instead of this:

getAdapter(data_model_object, IEntry, name="1.0")

We can now do this:

getMultiAdapter([data_model_object, request], IEntry)

Unfortunately, the benefits of this are mostly in the future. The two named lookups we do right now cannot be turned into multiadapter lookups. The first is the lookup that gets us the version-specific request interface in the first place. The second is a utility lookup:

root = getUtility(IWebServiceRootResource, name="1.0")

There's no such thing as a multi-value utility lookup. However, I'm considering writing a wrapper class that lets the utility lookup look like a simple adaptation:

root = IWebServiceRootResource(request)

But I'm not sure if that's valuable to the programmer.

To avoid a million test failures, I preserved the behavior of the unversioned code (where the incoming request does not have any special interface applied to it). I'll almost certainly remove this code once I make the service generation code support multi-versioning, but that's a way in the future.