[Qgis-developer] Value relations in QgsExpression

[Marco Hugentobler]

>Now thinking in a more generic way, a JOIN would JOIN two tables and not
>features. In that case (we possibly might end up supporting this kind of
>virtual tables e.g. from python plugins) a JOIN would then return a
>QgsFeatureIterator wrapped in a QVariant instead of a single tuple.
>I am not sure how exactly such a feature would be integrated yet, and
>how this interacts with the current expression engine (there are a
>couple of shared functionalities, but also some that are different),
>therefore I am also not sure if this should have any implications on the
>current implementation. So this paragraph is just thinking out lout.

Yes, that is the most generic way. Probably a bit overkill at the moment.

>That would be a join limited to certain attributes and my idea is that
>this would eventually be merged with the current JOIN functionality to
>remove duplicated work in this area.

Cool, this is certainly a very useful feature.

Regards,
Marco

-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee