successful write with If-Match can return stale values

[Gary Poster]

If you include an If-Match header when writing, such as with a PATCH, the cache can be populated with values that are not correctly cleared when changed.

This is because the FieldUnmarshallerMixin handles the _unmarshalled_field_cache in a naive way: it assumes that attribute names on an entry will be the same as on the context that it wraps. This assumption breaks with, for instance, a user's display name, which is display_name on the Entry but displayname on the user object itself. When the assumption breaks, changes are not noticed within the request, and return values are stale.

I have a fix locally that passes a Launchpad integration test where I discovered the problem. I will add a lazr.restful test and see if the tests pass with my change.

[Gary Poster (gary)]

Lines 368-382 of http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/view/12450/lib/canonical/launchpad/windmill/jstests/launchpad_ajax.js show that this is a regression, at least for a user's display_name. It was working when this Windmill test was part of Launchpad's suite. (I am in the process of rewriting these tests with our new YUI integration test machinery: see bug 724609.)