[Cubicweb] ComputedRelation

Christophe de Vienne christophe at unlish.com
Tue Mar 31 09:39:11 CEST 2015

Hi Sylvain,

Thanks for your answers.
I guess I will not (yet) use the ComputedRelation.



Le 31/03/2015 08:02, Sylvain Thénault a écrit :
> On 30 mars 23:05, Christophe de Vienne wrote:
>> Hi everyone,
> Hi Christophe,
>> I just did a few tests with ComputedRelation, and I have a some issues:
>> -   I could not find a documentation outside the CWEP 2 which is a bit
>>     light on the matter.
> There is though some documentation in the book about that.
> [syt at orion ~]$ rgrep ComputedRel src/cubicweb/doc/
> src/cubicweb/doc/3.20.rst:* virtual relations: a new ComputedRelation class can be used in
> src/cubicweb/doc/book/en/devrepo/datamodel/definition.rst:    class illustrator_of(ComputedRelation):
> src/cubicweb/doc/book/en/devrepo/datamodel/definition.rst:* nothing else may be defined on the `ComputedRelation` subclass beside
> But I don't remember if there are much more content than in the CWEP...
>> -   The '__permissions__' attribute is ignored. Whatever the value I
>>     set for the 'read' permission, DBG_SEC reveals that the match is
>>     always done against `set(['managers', 'users', 'guests'])`.
> According to the CWEP, this is a bug
>> -   The expression I would like to use requires a 'HAVING'
>>     clause, which gets lost in the final request. And it is, imo, a big
>>     limitation if not a bug.
>>     Is there any chance to add support for the 'HAVING' clause in a
>>     rule ? If so what delay can I expect it, given that I do not think
>>     I am in capacity to work on it ?
> One could ask if the problem is not rather the need for a HAVING clause in RQL,
> rather than allowing such restrictions in the WHERE clause...
> Anyway, I agree we want this in computed relation but unfortunatly can't commit
> on any time devoted to this topic for now.
>> -   As far as I know there is not, currently, any caching done on these
>>     computed relations. In our case, it would probably prove useful to
>>     have one (performance-wise).
>>     Is there any plan to add such a capability ?
> Yes, it was in the initial plans but we decided to not handle it at a first
> glance to keep things simple, because such a cache is somewhat hard to maintain
> (I suspect there are bugs in the computed attribute implementation for
> instance). Once we get the current implementation of computed relations and
> attributes properly working and some feedback, we may think again about that.

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