[Qgis-user] Field Calculator: dynamic calculations

[Alister Hood]

Hi,

> Date: Mon, 11 Jun 2012 10:45:07 +0200
> From: Peter Sch?rch <p.schuerch at meierpartner.ch>
> To: <qgis-user at lists.osgeo.org>
> Subject: [Qgis-user] Field Calculator: dynamic calculations
> Message-ID:
>         <3266F9F673EFF44BB345D5A707E32AC2919477 at meiwed1.meierpartner.local>
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> 
> Hi all,
> How would I implement a dynamic calculation with the field calculator? With dynamic I mean that the > result would change as values change in the input fields. With a Shape file, the result field obviously only contains the numerical result of any calculation and when the input changes I have to retype and re-execute the calculation in the field  calculator.
> In other GIS-Systems I have used this would be called a query.
> 
> Thanks for any input on this.
> Peter

I guess some providers (PostGIS and Spatialite?) might have a feature that allows this, but otherwise I don't think it is currently possible, except for labelling.  As I mentioned in another thread today, there was a discussion about implementing "virtual columns" using the same engine as the expression based labelling.  See http://lists.osgeo.org/pipermail/qgis-developer/2011-July/015383.html
You might want to look at helping implement it.

Regards,
Alister