Re: [xwiki-devs] [VOTE] Adding notions of Locale and Version in EntityReference

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 &lt;vincent(a)massol.net&gt; 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/cea424914f40ce924afbc49b3159… >>> ) >>>> : >>>> >>>> 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.h… >>>>> >>>>> 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.

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.

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,

fooling them into thinking all versions of every document are available in the same namespace,

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.

> 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.

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.