Re: [xwiki-devs] [Proposal][Model] Entity References - Absolute vs Relative

On Jan 3, 2010, at 1:49 PM, Thomas Mortagne wrote: I don't think we can compare with the filesystem. There's only one normalizing reference for the file system. This is not our case. Also I don't agree that API code should default to the current normalizer. This would mean the code will only work when there's a context doc and this puts some unnecessary restriction on the code. It's really the calling code that should pass the correct reference. I think (haven't thought enough about it though) I'd prefer to separate absolute reference from relative references so that apis that need an absolute ref can specify it in their signature. That would remove the need for checking + the need to throw an exception or use an arbitrary normalizer. We could also have a reference factory that takes an absolute ref and generate a relative reference (w/ default + current impl) for the user cases when you have an abs ref and need a relative one. Since our ref factory are typed we wouldn't even need a new interface. I need to think more about it but my feeling is that the absolute ref stuff we had before wasn't so bad after all. Maybe we just need to add a new notion of relative ref somehow for those few use cases requiring it but keep using absolute ref in most places. Thanks -Vincent >> My status: >> * I have implemented the normalizer code (both Default normalizer and >> current normalizer) >> * I'm now going to start re-implementing the entity reference >> factories and serializers >> * I'm looking at existing code to see how the code would need to be >> adapted and I'm finding that in several cases it's going to be hard. >> Just to illustrate this take this code: >> >> public String getAttachmentURL(AttachmentReference >> attachmentReference, boolean isFullURL) >> { >> String url; >> if (isFullURL) { >> XWikiContext xcontext = getContext(); >> url = >> xcontext >> .getURLFactory().createAttachmentURL(attachmentReference.getName(), >> >> attachmentReference >> .getDocumentReference().getLastSpaceReference().getName(), >> attachmentReference.getDocumentReference().getName(), >> "download", null, >> attachmentReference.getDocumentReference().getWikiReference().getName(), >> xcontext).toString(); >> } else { >> url = >> getAttachmentURL >> (this >> .entityReferenceSerializer >> .serialize(attachmentReference.getDocumentReference()), >> attachmentReference.getName()); >> } >> return url; >> } >> >> There's now no guarantee that the passed reference has a non null >> attachment name, space name or wiki name. The code would need to >> verify this (or createAttachmentURL() would need to check it but >> that's the same). What should it do if it finds a null name? It cannot >> guess if it should use the current normalizer or the default normalizer. >> >> The only solution I can see would be to check if the passed reference >> is absolute (using AttachmentReference.isAbsolute() for ex) and throw >> an InvalidEntityReference exception if it's not absolute. >> >> But that's going to be a pain probably... >> >> I'm still hesitating... >> >> WDYT? >> >> Thanks >> -Vincent >> >> On Dec 31, 2009, at 12:39 PM, Vincent Massol wrote: >> >>> Hi devs, >>> >>> I'm almost done with my entity reference refactoring and I've just >>> realized I have missed something I think. So far the implementation >>> only supports Absolute references (i.e the entity reference factory >>> always return a reference with all parts filled - you choose to use >>> a default factory or a current entity depending on how you wish to >>> resolve the names when they have not been provided in the passed >>> reference string). >>> >>> I now think we must also support relative references (i.e. when some >>> parts can be null) and that it's up to the user of the api to decide >>> if they want to convert a relative reference to an absolute one or >>> not. >>> >>> Here's a use case: renaming of documents. For exemple documents have >>> links specified as a string representing the target doc name. If we >>> don't have relative references then we need to decide if we want to >>> use the default serializer (all parts printed including wiki name) >>> or the compact serializer (only parts different from context >>> reference printed). This doesn't support printing only what the user >>> had decided to fill. For ex a user might have specified voluntarily >>> the space and page name and right now with my implementation he'll >>> get only the page name specified if the new space is the same as the >>> space for the current doc. >>> >>> So here's my proposal: >>> >>> * Entity Reference Factory leaves parts to null when not specified >>> in the string representation. >>> * We add a EntityReference.getAbsoluteReference(EntityReference >>> base) method to return an absolute reference. It's resolved against >>> the passed base reference (i.e. parts not specified are taken from it) >>> >>> WDYT? >>> >>> I'm going to start refactoring my code to do this later today so >>> please let me know if you see any pb with it. >>> >>> Thanks >>> -Vincent