Hi Matthias,ah, that makes a lot of sense. So this can be used as a hint for optimisation of the ~"bandwidth" of the function so to speak. What a cool feature! My dataset was a tiny local geopackage so no surprise it just gave me access to all columns straight-away.
When I find time to make a PR I'll add a clearer sentence to the documentation and to change the new function template to either remove the parameter (so it uses the default) or make it use QgsFeatureRequest.ALL_ATTRIBUTES explicitely as hint that one could optimize that. (I prefer to remove it, it's optional with a sensible default...)
Cheers Hannes Am 22.11.21 um 14:48 schrieb Matthias Kuhn:
Hi Hannes,This information can be used by the expression engine to determine what needs to be requested from the provider. This can lead to significant performance improvements, depending on the scenario.Depending on other functions used in the expression and the capabilities of the provider itself, the request may or may not include them.As stated in the help, it's what the function *requires*, these attributes are guaranteed to be available. Others may still be there.Cheers MatthiasOn Mon, Nov 22, 2021 at 2:41 PM Johannes Kröger (WhereGroup) <johannes.kroe...@wheregroup.com <mailto:johannes.kroe...@wheregroup.com>> wrote:Hi list, https://docs.qgis.org/3.22/en/docs/user_manual/expressions/expression.html#function-editor <https://docs.qgis.org/3.22/en/docs/user_manual/expressions/expression.html#function-editor> mentions the optional keyword argument "referenced_columns" to the `@qgsfunction` decorator. It says > referenced_columns=[list]: An array of attribute names that are required to the function. Defaults to > [QgsFeatureRequest.ALL_ATTRIBUTES]. That, and examples where it is used in other people's code, led me to believe that the feature's attributes would not be accessible unless listed in that parameter or if the parameter was omitted (-> default value getting used -> default is all attributes). The default code that gets inserted into the editor includes the decorator `@qgsfunction(args='auto', group='Custom', referenced_columns=[])` so I'd assume that I would not be able to use any attributes in the function. In reality I can access them just fine though, e. g. `feature["name"]` if I had features with a "name" attribute and that default `referenced_columns=[]`. I can even do so if I used `referenced_columns=["foo", "bar"]`! `feature["name"]` is still perfectly accessible. Is this a bug or by design? If by design, what purpose does this parameter have? Thanks Hannes-- Johannes Kröger / GIS-Entwickler/-BeraterWhereGroup GmbH Eifelstraße 7 53119 Bonn Germany Tel: +49 (0)228 / 90 90 38 - 36 Fax: +49 (0)228 / 90 90 38 - 11 johannes.kroe...@wheregroup.com <mailto:johannes.kroe...@wheregroup.com> www.wheregroup.com <http://www.wheregroup.com> Geschäftsführer: Olaf Knopp, Peter Stamm Amtsgericht Bonn, HRB 9885 ------------------------------- ******************************************** Where2B Konferenz 2021 16. Dezember 2021 im Universitätsclub Bonn und online https://where2b-conference.com/ <https://where2b-conference.com/> ******************************************** _______________________________________________ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org <mailto:QGIS-Developer@lists.osgeo.org> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer <https://lists.osgeo.org/mailman/listinfo/qgis-developer> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer <https://lists.osgeo.org/mailman/listinfo/qgis-developer>
-- Johannes Kröger / GIS-Entwickler/-Berater WhereGroup GmbH Eifelstraße 7 53119 Bonn Germany Tel: +49 (0)228 / 90 90 38 - 36 Fax: +49 (0)228 / 90 90 38 - 11 johannes.kroe...@wheregroup.com www.wheregroup.com Geschäftsführer: Olaf Knopp, Peter Stamm Amtsgericht Bonn, HRB 9885 ------------------------------- ******************************************** Where2B Konferenz 2021 16. Dezember 2021 im Universitätsclub Bonn und online https://where2b-conference.com/ ********************************************
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