28 Mar
2012
28 Mar
'12
10:49 a.m.
On Wed, Mar 28, 2012 at 09:42, Vincent Massol <vincent(a)massol.net> wrote:
Thanks to Thomas and Denis for the explanations. I
understand now, it's
very clear :)
However I'd like to suggest a different solution.
Premises:
* 99% of the use cases are for relative references
Right, since nothing else would work today.
* We need to make sure devs don't use the API
wrongly and thus the API has
to be easy to use right
This is true for most API, maybe we could add more helpers, but this is not
the subject of this vote.
* We have never supported absolute references to
XClasses (since we've
never supported this in the DB)
The database have never support it, but the whole API have been written to
support it. This has been the result of a previous vote on this subject.
This is why we have not proposed to change the behavior of the API, but a
temporary solution to help those that have use it badly and was never able
to notice it due to some bug at store level, that this usage is currently
wrong, and fix it on the fly for now (quick fix), since there is no other
valid usage for our current storage.
Based on these premises I'd like to suggest that:
* We automatically remove the wiki part when adding an XObject
(specifically in resolveClassReference())
We effectively propose to do so with a stack trace warning if the wiki is
ok, and with a stack trace error if you try to really link to an external
class. This would not break abruptly existing wrong usage, and allow us to
extends later.
* Later on when we implement a new storage that
supports multiwiki for
xclasses then we add another method so that users who want to use an
absolute reference do it voluntarily and not by mistake. It could be:
newAbsoluteXObject(…) for example. Alternatively we could add:
newXObject(EntityReference ref, boolean isAbsolute).
This is not that simple. We take care of relativizing the reference in most
places already, before calling object creation.
But, for sure this would simplify a lot. This means removing what we have
done up to now. However, we support external classes in all places from the
action, and only the storage does not really allow them. Should we revert
that ?
On the other hand, this seems to me curious to pass over an absolute
reference to just ignore a part of it. Maybe we are simply missing
something in references to helps these usages ?
This will ensure that users of the api can't use
it wrongly.
I really don't see any point in continuing to try to support a feature
that doesn't exist and that we can't support… It's better to add support
for it when we implement a storage that supports it.
Thanks
-Vincent
On Mar 26, 2012, at 8:07 PM, Thomas Mortagne wrote:
wiki.
--
Denis Gervalle
SOFTEC sa - CEO
eGuilde sarl - CTO
On Mon, Mar 26, 2012 at 6:21 PM, Vincent Massol
<vincent(a)massol.net>
wrote:
> Hi,
>
> This looks like a very complex topic. Trying to answer below (or rather
ask
questions)…
>
> On Mar 26, 2012, at 3:43 PM, Thomas Mortagne wrote:
>
>> Hi devs,
>>
>> we have an important inconsistency that we ignored since a long time
>> and that is producing http://jira.xwiki.org/browse/XWIKI-7628.
>>
>> The main issue is that the storage save document containing object
>> linked explicitly to another wiki without complaining which mean that
>> user continue using API wrongly without really knowing it's wrong. And
>> now we have lots of code badly using object class related API and
>> contently creating object with absolute class references.
>
> I don't see anything wrong with adding an XObject to a Document using
an
absolute XClass reference. This is actually the API we've added and
we've only added relative XObject API more recently which IMO is the wrong
one since we always said we wanted to use absolute references everywhere in
all APIs and it's up to the storage to remove/add the wiki part.
Are we talking about the same thing?
It's not that simple, xclass reference in xobject are working like
parents reference in document: they are relative to keep what the user
explicitly asked even when the document is copied in another context.
So which reference is set to the object is very important because the
reference will be copied as it is when copying a document.
Here is the javadoc you wrote in BaseCollection:
/**
* The meaning of this reference fields depends on the element
represented. Examples:
* <ul>
* <li>If this BaseCollection instance represents an XObject then
refers to the document where the XObject's XClass
* is defined.</li>
* <li>If this BaseCollection instance represents an XClass then
it's not used.</li>
* </ul>
* Note that we're saving the XClass reference as a relative
reference instead of an absolute one. This is because
* We want the ability (for example) to create an XObject relative
to the current space or wiki so that a copy of
* that XObject would retain that relativity. This is for example
useful when copying a Wiki into another Wiki so
* that the copied XObject have a XClassReference pointing in the new */
private EntityReference xClassReference;
It's not only a storage issue, if you have an document object with
reference wiki1:Space:MyClass and copy that document to wiki2 then you
will have an object in wiki2 with class wiki1:Space:MyClass. The
storage does not have a word to said in this process it just get the
resulting new XWikiDocument to save and in this case we are asking the
store to store an object defined by a class which is in another wiki,
something that it does not support and more importantly something that
was not intended.
So we have several choices here:
1) continue hiding under the carpet that we are asking to the store
something that it can't do and have inconsistency between object and
storage and crappy hack here and there in the storage (in the case of
XWIKI-7628 it means not trusting what's returned by
BaseObject#getReference)
2) totally forget about relative xclass reference chosen outside of
BaseObject and always remove the wiki from the reference stored in
BaseCollection#xClassReference which mean that this API will
officially never support having an object with a class from another
wiki
3) keep the current API as it has been defined and voted and try to
make a bit more sure people are using it the way it's supposed to be
used
Here we are talking proposing 3)
Got it!
>> Until now it was OK even if a mess and
it's still not visible. But
>> that's mostly luck... until we start copying documents from one wiki
>> to another starting with 4.0 branch. What changed is that the
uniquetemporary
>> identifier of the object in the database
is "properly" generated by
>> using it's reference and since a class reference in a BaseObject
>> contain a wiki it's now taken into account. The old id generator used
>> to use the deprecated BaseCollection#getClassName which is forced
>> absolute for retro-compatibility reason even if it was actually
>> possible before to put absolutely anything as class reference.
>>
>> So right now we have two issues:
>> * store save invalid document without complaining
>> * many code is wrongly using BaseObject and XWikiDocument API
>> regarding class references mostly because you don't really see it
>> right away when you don't use it properly. Even ObjectAddAction is
>> wrong, a lot of code that was using setClassName has been badly
>> converted to fix deprecated method code by resolving what was passed
>> to setClassName into an absolute reference which is very wrong and not
>> the behavior of setClassName.
>>
>> Here is what we propose with Denis:
>> * 4.x (or until class coming from another wiki is supported but I
>> doubt this is going to happen anytime soon with this storage):
>> ** throw an exception in the storage when saving a document containing
>> objects coming from another wiki
>
> I don't like this. If the problem is that we don't want to allow an
XObject to be added when the XClass is coming from another wiki then this
should be checked at the level of the AddXObject APIs and throw an
exception there.
This has nothing to do with what we propose, the goal here is to find
code which is setting absolute reference for the class to that it's
fixed to not have issue when copying. If we do what you say then the
document copy will fail like it does now but simply for another reason
and it's not going to help fixing anything because the issue is not at
this level but in the code that put an absolute reference in the
original document.
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Thanks
-Vincent
--
Thomas Mortagne
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http://lists.xwiki.org/mailman/listinfo/devs ** to temporary limit breakage while we fix wrong
code and help us
find this wrong code, modify BaseCollection#setXClassReference to
force it to remove the wiki from the passed reference and log a
warning about a bad usage
* 5.0: remove the bandage from BaseCollection#setXClassReference
WDYT ?
Here is my +1
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