On Dec 21, 2010, at 1:23 PM, Henning Eggers wrote: > Hi, > I have been trying to figure out how adapter look-up works in Zope. Please > consider this example: > > http://paste.ubuntu.com/546342/ > > It turns out that the returned adapter depends on the order in which the > interfaces are mentioned in the "implements" statement of "MyImplementation". > QueryAdapter will always return the adapter to the first interface in the > list, in this face "MyAdapterA". > > It would be interesting to know if this behavior is intended and > deterministic.
Yes. The first is always regarded as the most important, in this and other aspects. > > This has bearing on our security policy though (which is why I was trying to > figure this out). In my case this translates as follows: > > ITarget = IAuthorization > InterfaceA = IHasCustomLanguageCodes > InterfaceB = IProduct > the_name = launchpad.TranslationsAdmin (the named permission) > > The IAuthorization objects in security.py get registered as adapters from > "<usedfor>" to IAuthorization, named "<permission>". With the behavior I > identified here, it follows that the selection of the security policy depends > on the order in which the "implement" statement of the "Product" class lists > interfaces. In this case, the Adapter for IHasCustomLangugeCodes shadows the > adapter for IProduct because that list is sorted alphabetically AFAICT. I'm not familiar with anything alphabetical being involved. > > I was not aware of this. Is everybody else? Is this intended? Is this good? I think it is good for the adapter registry: it is a simple rule that can be relatively easily reasoned about, as opposed to something with more heuristics. In this context, I've never done a thoughtful survey of Launchpad's security machinery, and don't have a concrete opinion as to its usage of the adapter machinery. It sounds like a "Gotcha" at best, in this context. Gary _______________________________________________ Mailing list: https://launchpad.net/~launchpad-dev Post to : [email protected] Unsubscribe : https://launchpad.net/~launchpad-dev More help : https://help.launchpad.net/ListHelp
