[Qgis-user] relation_aggregate

[Thayer Young]

 Hi Graeme,
I think this may be a bug, it appears that this worked at some point, 
https://gis.stackexchange.com/questions/222625/qgis-relation-aggregate-how-does-this-work#238265
The QEP referenced above is still open:
QEP 59: Aggregate functions for QGIS expressions · Issue #59 · qgis/QGIS-Enhancement-Proposals
but it may not be working anymore?https://github.com/qgis/QGIS/issues/29115
I tried dumping the expression results to a field in field calculator. I am able to get output only by referencing field names that are common in both the 1 and the many table, for example using the relation between Canadian Provinces and Regional Districts, only the province UID gives anything besides NULL:
relation_aggregate('RDs_in_Provinces','concatenate',"PRUID")

-Thayer


    On Wednesday, April 6, 2022, 07:40:08 AM EDT, qgis-user-request at lists.osgeo.org <qgis-user-request at lists.osgeo.org> wrote:  
> PUBLIC


> Hello,

> I am having issues getting relate_aggregate to do anything within expression builder. Ideally, I would like a features (1) to (m) attributes table setup correctly with a relationship to allow a user to select attributes based on attribute criteria have the corresponding related features selected / shown on map as related. Given how little I am uncovering online about ways to do this, it might not be possible, but even getting the expression builder to update a field in my features with a count of corresponding values in attributes is not updating feature's values, I am wondering if I am doing something wrong. Should this work?

> Within select by attributes for the feature table:
> relation_aggregate( 'relation _ID','count',1) > 3

> The preview of the expression returns a value for a feature (without the >3 at end), but when I try to calculate a field of this count - every value returns NULL. With the >3 it does not work at all to select anything.

> It does look like 'relation_aggregate( 'relation _ID','count',1)' is fine for the basis of evaluating a field of values based on preview but it returns null on running the field calculator.

> I am using QGIS 3.16

> Regards,
> Graeme


> PUBLIC

  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20220406/fab31a23/attachment.html>