On 11/16/2011 03:14 AM, Vincent Massol wrote:
>
> On Nov 16, 2011, at 6:51 AM, Caleb James DeLisle wrote:
>
>>
>>
>> On 11/15/2011 03:26 PM, Vincent Massol wrote:
>>>
>>> On Nov 15, 2011, at 9:04 PM, Caleb James DeLisle wrote:
>>>
>>>
>>>> On 11/15/2011 12:25 PM, Vincent Massol wrote:
>>>>>
>>>>> On Nov 15, 2011, at 5:29 PM, Denis Gervalle wrote:
>>>>>
>>>>>> On Tue, Nov 15, 2011 at 17:11, Vincent Massol <[email protected]> wrote:
>>>>>>
>>>>>>>
>>>>>>> On Nov 15, 2011, at 5:03 PM, Denis Gervalle wrote:
>>>>>>>
>>>>>>>> Hi Devs,
>>>>>>>>
>>>>>>>> The implementation of the immutable version of reference is almost
>>>>>>>> ready
>>>>>>>> now. It introduce the parameters on reference as suggested, but we now
>>>>>>> have
>>>>>>>> a discussion on how the constructors of "typed" entity reference should
>>>>>>> be.
>>>>>>>>
>>>>>>>> My initial dev was to provide constructor like:
>>>>>>>
>>>>>>> you're missing something here :)
>>>>>>>
>>>>>>>> But Vincent have different vision of this, here its comment extracted
>>>>>>> from
>>>>>>>
>>>>>>> I don't have a different vision. It's just that you limited your
>>>>>>> proposal
>>>>>>> to just Locale which clearly isn't good enough.
>>>>>>>
>>>>>>>> GitHub (
>>>>>>>>
>>>>>>> https://github.com/xwiki/xwiki-platform/commit/cea424914f40ce924afbc49b3159bc8934251aac#commitcomment-721603
>>>>>>> )
>>>>>>>> :
>>>>>>>>
>>>>>>>> My proposal was:
>>>>>>>>> - generic params in EntityReference
>>>>>>>>> - helpers methods for get/setLocale and get/setVersion in
>>>>>>> DocumentReference
>>>>>>>>>
>>>>>>>>> Now the fact that we're making the refs immutable changed this since
>>>>>>> it's
>>>>>>>>> no longer possible.
>>>>>>>>>
>>>>>>>>> I don't think multiplying the constructor signatures is a good idea.
>>>>>>>>>
>>>>>>>>> We could either have:
>>>>>>>>>
>>>>>>>>> public DocumentReference(String wikiName, List spaceNames, String
>>>>>>>>> pageName, Map<String, Object> parameters)
>>>>>>>>>
>>>>>>>>> or
>>>>>>>>>
>>>>>>>>> public DocumentReference(String wikiName, List spaceNames, String
>>>>>>>>> pageName, Pair<String, Object>... parameters)
>>>>
>>>> Neither of these signatures will work, If you want storage to have any
>>>> hope of being able to get the same object for the same reference, it must
>>>> be at least
>>>> a Map or Pair of <String, Serializable>, if you allow people to pass
>>>> transient objects such as TCP sockets, they will.
>>>>
>>>> More importantly, if you introduce another parameter, there will be no way
>>>> to search for all documents where param X = value Y. To do it with SQL
>>>> would require
>>>> an evil query which did text searching on the parameter field something
>>>> like: WHERE doc.reference LIKE '%param=value%'
>>>> To add parameters to a reference and retain the ability to get all
>>>> documents where "param=value" you would have to modify the database schema
>>>> unless the information
>>>> already exists in the XWikiDocument mapping as with language.
>>>>
>>>>>>>>>
>>>>>>>>> where Pair is
>>>>>>>>>
>>>>>>> http://commons.apache.org/lang/api-3.0-beta/org/apache/commons/lang3/Pair.html
>>>>>>>>>
>>>>>>>>> Maybe this needs some discussion on the devs list rather than here to
>>>>>>> make
>>>>>>>>> sure everyone sees it?
>>>>>>>>>
>>>>>>>>
>>>>>>>> I am myself not really happy with that since I dislike the idea that
>>>>>>>> parameter are generic on "typed" references.
>>>>>>>> Do not like either the idea to provide keys for creating a Map or
>>>>>>>> Pairs,
>>>>>>>> since the implementation details that use Map should not be so exposed
>>>>>>> IMO.
>>>>>>>>
>>>>>>>> There should not be so much parameter on a single "typed" reference,
>>>>>>>
>>>>>>> I don't understand this sentence.
>>>>>>>
>>>>>>> The Map is <String, Object>.
>>>>>>>
>>>>>>
>>>>>> I would means that this should not cause so many additional constructors,
>>>>>> if we list them individually.
>>>>>> So your have not the same vision then I have :)
>>>>>
>>>>> See below.
>>>>>
>>>>>>>> and
>>>>>>>> these should be easy to provide. Creating Maps in java is not fun in
>>>>>>> syntax
>>>>>>>> for that IMO, and is far too open.
>>>>>>>
>>>>>>> Sure but the goal here is not to redo java…
>>>>>>>
>>>>>>
>>>>>> Not my goals, just want to be explicit and easy to use.
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>> I had propose using overloaded constructor like
>>>>>>>>
>>>>>>>> public DocumentReference(String wikiName, List<String> spaceNames,
>>>>>>>> String
>>>>>>>> pageName, Locale locale)
>>>>
>>>> +1
>>>>
>>>>>>>
>>>>>>> Again, this doesn't work. It only works for a **single** parameter. It
>>>>>>> doesn't work for multiple parameters. How do you specify the Locale or
>>>>>>> some
>>>>>>> unknown String param?
>>>>>>>
>>>>>>
>>>>>> I simply provide the need constructor, no more.
>>>>>
>>>>> If you say this then you say that we don't need generic parameters for
>>>>> References which is what started the discussion…
>>>>>
>>>>> Also what you say is not correct at all since we already know we need
>>>>> Version which you didn't put.
>>>>>
>>>>> Last, it means passing null to the constuctors when you don't use the
>>>>> parameters which is really really bad IMO or you'll need to define lots
>>>>> of various constructors which increase exponentially with the number of
>>>>> parameters we support.
>>>>
>>>> A constant need for new parameters indicated design problems, including
>>>> locale information is fixing an error which limited the document reference
>>>> from the beginning.
>>>> Building this infrastructure for additional parameters will foster bad
>>>> practice of using parameters where spaces should be used instead and will
>>>> allow the creation
>>>> of arbitrary dimensional data trees where users are only familiar with the
>>>> standard 1 dimension of filesystems and URLs.
>>>>
>>>>>
>>>>> However this won't even work since you won't be able to support adding
>>>>> new parameters. Users of the Reference system will need to modify its
>>>>> source if they wish to add a new parameter which again goes against the
>>>>> initial proposal.
>>>>>
>>>>>>>> or if something more flexible should be used
>>>>>>>>
>>>>>>>> public DocumentReference(String wikiName, List<String> spaceNames,
>>>>>>>> String
>>>>>>>> pageName, Object... parameters)
>>>>>>>>
>>>>>>>> where parameters is later interpreted based on object type and limited
>>>>>>>> to
>>>>>>>> those used for a given typed reference.
>>>>>>>
>>>>>>> This doesn't work. If I have 2 parameters of type String, how do you map
>>>>>>> them automatically?
>>>>>>>
>>>>>>
>>>>>> I suggest not to have loosely typed parameters, but strong one, like
>>>>>> Locale
>>>>>> and Version.
>>>>
>>>> +1
>>>>
>>>> I am -1 on version, I don't like it since a document history should be a
>>>> separate entity which yields documents, as it is now.
>>>
>>> How do you reference a given version of, say, a document? And how do you
>>> pass this along the chain of calls?
>>>
>>> We'll need to introduce a new Reference (which is the initial reason I made
>>> this proposal - I had to introduce a UniqueReference class in the new Model
>>> before of this).
>>
>> If you are needing to reference old versions of something on a regular basis
>> then you are going to run into performance issues.
>> We only access old versions either via a look at them or to rollback, both
>> operations which we accept will be slow.
>
> I don't understand what this changes. If you're able to "look at them" then
> it means you have the logic to … look at them. The fact that you can have a
> reference to that version doesn't change anything.
>
> Also I don't agree about performance. That only depends on how versions are
> stored in the storage.
My apologies again for being vague, we generally only access old versions of
through the viewrev action and the rollback action.
This is for a good reason, accessing old versions of documents is hard because
we don't store entire versions of old documents, we store differences between
versions.
All versioned data stores function this way for space efficiency but it incurs
a performance penalty on loading old versions.
IMO it's important to help the user understand this performance penalty by
making them use a special call to get old versions.
>
>
>
>>
>>>
>>>> If we include version in the reference, storage will be forced to remove
>>>> it on save because we want users asking for a document
>>>> with no knowledge of the current version to get the current version. This
>>>> means we already have a magic attribute which is treated
>>>> differently by storage.
>>>
>>> All params are treated specially by the code, I don't understand what's the
>>> problem. The exact same thing will happen for the Locale.
>>
>> On a storage level, you can take the reference, serialize it into a UUID
>> then lookup the document with that UUID.
>
> No that's not true. Right now for example we remove the wiki part of the
> reference since we have one DB per wiki.
Indeed, how to map wikis to databases in the future is another topic for a
different discussion, FWIW I don't think the current system is optimal.
As a side note, the wiki reference is a very central part of the
EntityReference, far from an arbitrary parameter which happens to be under the
key "VERSION".
>
> Saying that a reference is stored as is in a "Document row" (assuming RDBMS
> for the sake of the discussion) is not correct IMO. That's not the role of a
> reference. A reference is computed based on various parts (wiki it's in,
> space it's in, locale, revision, etc).
>
>> If a version parameter is added, the storage has to remove that parameter
>> first.
>
> The reference is never stored in the storage as is! When an Entity is loaded
> from the storage the reference is computed based on various things. For
> example as I explained above, based on the DB name for the wiki part.
I think we should be moving toward a new storage system which does simply store
the entire reference for performance and code cleanliness in the store.
>
>>>> In addition, the introduction of a version parameter will allow a user to
>>>> load a document of a given version
>>>> with a simple getDocument() call,
>>>
>>> Yes that's the idea! :)
>>>
>>>> fooling them into thinking all versions of every document are available in
>>>> the same namespace,
>>>
>>> Not sure what namespace you're referring to.
>>
>> Namespace is the wrong word, you tell the user that it's coming from the
>> same place but it's not.
>>
>> Consider this:
>> thirdVersion = xwiki.getDocument(referenceToThirdVersionOfMainWebHome);
>> thirdVersion.setContent("new content");
>> thirdVersion.save();
>> println(xwiki.getDocument(referenceToThirdVersionOfMainWebHome).getContent());
>>
>> This will not yield the new content, if it did then the versioning system
>> wouldn't really be versioning.
>> But by treating a version as a distinct document with a distinct reference,
>> you are telling the user that it should.
>
> errr? This is a completely different problem. It's about immutability or not
> of past revisions.
>
> Consider what we do now:
>
> currentVersion = xwiki.getDocument(refereneToCurrentVersionOfMainWebHome)
> thirdVersion = currentVersion.getVersion(thirdversion)
> thirdVersion.setContent("new content")
> thirdVersion.save()
>
> currentVersion = xwiki.getDocument(refereneToCurrentVersionOfMainWebHome)
> thirdVersion = currentVersion.getVersion(thirdversion)
> println(thirdVersoin.getContent());
>
> How is that different?
>
> What do you propose?
I'm not making a proposal right now but I do believe in weighing different
options.
User interface is everything and this is user interface, even if it is
interface for advanced users.
What we currently do gives the user a small heads up that something is
different because the old version "comes from" the new version but I agree it
is inadequate.
Off the top of my head I can imagine something like:
currentVersion = xwiki.getDocument(refereneToCurrentVersionOfMainWebHome)
currentVersion.asVersion(3.0);
println(currentVersion.getContent());
currentVersion.save();
With asVersion() not returning a distinct document but switching the document
underneath the wrapper which the user sees, the user never thinks he is
modifying an old version.
If we are going to make old versions mutable after the fact, this will require
a separate proposal as it raises another set of issues.
>
>>>> if getDocument(referenceToThirdVersionOfMainWebHome) works then it stands
>>>> to reason that search("WHERE doc.version=3 AND doc.name='Main.WebHome'")
>>>> would as well but it won't because that's not how storage works.
>>>
>>> Maybe you meant that it's not how storage currently work?
>>>
>>> Remember that this proposal has nothing to do with either the current model
>>> or the current storage. It's about the new model and the new storage that
>>> we want to have.
>>
>> I don't understand what you mean by this.
>> Inserting a new row into the document table every time a user edits a
>> document is not feasible.
>>
>>>
>>>>> I'm a big big big -1 on this.
>>>>>
>>>>> There's no reason to create a fake String when all you need is a string.
>>>>> Same for int, long, Number, etc.
>>>>> Same for also if you want to have several Locales or several Versions.
>>>>>
>>>>>>> Also the goal is to have unknown parameters so how can you do a mapping
>>>>>>> for something unknown? :)
>>>>>>>
>>>>>>
>>>>>> That is clearly not my goal, why do you want unknown parameters on
>>>>>> Document
>>>>>> Reference ?
>>>>>
>>>>> Maybe this is where we don't agree. This is the original idea: to have a
>>>>> set of "unknown" parameters for extensibility (from the POV of the
>>>>> Reference of course, from the POV of XWiki they are not unknown obviously
>>>>> ;)). This means that it's up to the users of the References to decide
>>>>> what parameters to put and it's up to the consumers to decide what
>>>>> parameters to support.
>>>>
>>>> The introduction of k-d trees for storing documents is not something that
>>>> anyone has ever used to my knowledge, it may be something that people
>>>> think they need
>>>> but like the goto command, something that starts out nice ends up creating
>>>> more problems than it's worth.
>>>>
>>>>>
>>>>> It seems to me your vision is to:
>>>>> * Not support arbitrary parameters
>>>>> * Only support Version and Locale
>>>>> * Provide 3 constructors, one where there's no Locale no Version, one
>>>>> with Locale no version and one with Version on Locale
>>>>>
>>>>> Whereas my vision is:
>>>>> * Support arbitrary parameters for extensibility (like a URL if you
>>>>> prefer which support arbitrary parameters)
>>>>
>>>> This is not correct, the parameters in a URL are never to my knowledge
>>>> used as a discriminator.
>>>> Any webserver I can think of uses the parameters as arguments which are
>>>> passed to the page, not discriminators to select the page.
>>>
>>> Fun, you forgot XWiki itself! :)
>>> We use version and language as URL parameters…. ?rev=X&language=Y
>>>
>>> Params reference are optional and are meant to be qualifier for the
>>> reference.
>>
>> IMO this is a bad design since it means that certain parameters such as
>> language have special meanings, all others are used as a means of
>> communicating with the scripting in the wiki page.
>>
>>>
>>>> for example:
>>>> path/to/some/page.php?var=val&varb=42
>>>> will load the page "path/to/some/page.php" then execute it, passing
>>>> var=val and varb=42 as arguments.
>>>
>>> Seen all this I propose that stop this discussion and don't commit any of
>>> this on master for the moment since we have too many diverging opinions on
>>> the new model and we need to agree about the new model first.
>>>
>>> So I change my vote about the proposal I initially sent to -1 for now till
>>> this is sorted out because I don't want to rush into something for which we
>>> don't agree and have diverging ideas.
>>>
>>> I've been planning to put the work I started in the contrib sandbox into a
>>> branch on master in order to start using it ASAP (Thomas and I had a
>>> discussion and we think we could already start to slow use portions of it
>>> to validate it).
>>>
>>> So here's what I propose:
>>>
>>> * I do this ASAP
>>> * I write an email explaining the work done so far on the new model
>>> * We discuss it and come to an agreement
>>> * Whether we extend our current Entity References with params or not will
>>> be a direct consequence of the model agreement
>>>
>>> I know Denis wanted to use the Locale param for his work. FTM Denis will
>>> have to pass the Locale as a parameter alongside the Entity Reference as
>>> it's done every where ATM.
>>>
>>> Is that ok?
>>
>> I disagree with slamming on the brakes on Denis's branch, the Denis wrote a
>> lot of code with the understanding that everyone agreed on it so I want to
>> do that justice.
>> I have reviewed Denis's branch and it all looks good to me, it makes 2 major
>> changes:
>> 1. Immutability which I have wanted since early on, I think this will make
>> the code a lot more stable.
>> 2. Introduction of a locale field which is necessary for the reference to be
>> able to map to a document id, this means we need it now in order to make new
>> references compatible with the existing model.
>>
>> The other proposals such as version and arbitrary parameters broaden the new
>> model over the existing one and they should not be undertaken without
>> research into how the new model will interact with users and new storage, as
>> well as how it will interact with old storage and the old model during the
>> transition.
>>
>> In my review of the branch, I found a few things which could be changed:
>> In EntityReference.java:
>>
>> private static final long serialVersionUID = 1L;
>> that should become 2L because removing child is a breaking change from a
>> serialization standpoint.
>>
>> public EntityReference(String name, EntityType type, EntityReference parent,
>> Map<String,Object> parameters)
>> I think this should be protected at least for now.
>>
>> public final Object getParameter(String name)
>> I think this should be protected at least for now.
>>
>>
>> +1 for merging the branch with these changes.
>
> I'm also ok to just add support for Locale right now but I really hope we'll
> agree in the future because there's no reason to consider locale differently
> than the version for example IMO.
>
> Also I'd like that Denis remove the Map of parameters in EntityReference
> since this is not going to be used and we need an agreement first about them
> which we don't have ATM.
>
> This means moving the getLocale() to EntityReference and having a specialized
> constructor for taking a Locale in EntityReference.
IMO locale is an attribute of a DocumentReference, not an EntityReference. It
makes no sense to have a Spanish object in an English document,
objects/attachments could indicate their locality by which document they are
attached to.
My opinion aside, I think we should stick to what is needed to make the new
reference model able to represent the old data model and right now, we only
translate documents.
I don't have a strong position on how the internals work, and I will defer to
Denis's judgement on that matter.
>
> Of course we all realize that this means that if we agree in the future about
> adding the Version or other params we're going to break APIs once more
> because we'll need to add new constructors, possibly deprecate old ones and
> add new methods, but I don't see any other way if Denis really wants to have
> this now.
These APIs are still young, to really get this right we'll will need a few
feedback cycles before we really know what we need.
Caleb
>
> Thanks
> -Vincent
>
>> Caleb
>>
>>
>>>
>>> Thanks
>>> -Vincent
>>>
>>>> Caleb
>>>>
>>>>
>>>>> * Have some "well-known" parameters so that xwiki code that users
>>>>> References know what they can put as reference parameters and what they
>>>>> can extract from XWiki parameters.
>>>>>
>>>>> Thanks
>>>>> -Vincent
>>>>>
>>>>>>> Thanks
>>>>>>> -Vincent
>>>>>>>
>>>>>>>> Here Vincent comments on this:
>>>>>>>>
>>>>>>>>> The automatic mapping idea seems a bad idea to me (too magic and
>>>>>>>>> doesn't
>>>>>>>>> work in a lot of cases).
>>>>>>>>
>>>>>>>>
>>>>>>>> Maybe some of you have an even better idea ?
>>>>>>>>
>>>>>>>> Denis
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