[QGIS-Developer] QGIS field calculator: issue with updating selected only features in combination with virtual field

[Denis Rouzaud]

Hi Andreas,

Here is a PR for a fix https://github.com/qgis/QGIS/pull/33101

Denis

Le mer. 27 nov. 2019 à 11:34, Andreas Neumann <a.neumann at carto.net> a
écrit :

> Hi Denis,
>
> But it is currently broken - right?
>
> If I go to field calculator on a read only PG layer, I can only create
> "Virtual fields" no "Physical fields", because my layer is read only (this
> is expected). However, the checkbox to only update the "xx selected"
> features is activated by default and not greyed out. And I can toggle the
> Checkbox, although it has no effect and is misleading.
>
> I just tested it in 3.4.x and 3.10.
>
> I can open an issue on it.
>
> Andreas
>
>
> On 2019-11-27 08:35, Denis Rouzaud wrote:
>
> Hi Andreas,
>
> It does sound like this is the current status today: the "update only..."
> checkbox is disabled if you create a virtual field.
> It seems Matthias ;) coded it in 2014:
> https://github.com/qgis/QGIS/commit/68de043ecbcf0203b6a3667b488be71f479e5d91#diff-ff2f9c5bc35d79bfe1f0b7690bc60819R344
>
> Cheers
>
> Le mer. 20 nov. 2019 à 13:12, Matthias Kuhn <matthias at opengis.ch> a
> écrit :
>
> Hi Andreas,
>
> On first sight I'd also say that disabling the checkbox is the right thing
> to do.
>
> For the other proposed behavior the requirements seem unclear (i.e. should
> the selection be preserved or the values changed when the selection
> changes), so we need a specific use case where this is required to take a
> decision.
>
> Best regards
>
> Matthias
> On 11/20/19 11:27 AM, Andreas Neumann wrote:
>
> Hi,
>
> We came across an inconsistency in the field calculator:
>
> One can select the checkbox "Only update xx selected features" in
> combination with creating a new virtual field. This is quite misleading for
> the user, as the result is that all features (not only the selected ones)
> are updated.
>
> I see the following solutions:
>
> - disable the checkbox "only update xx selected features" as soon as a the
> field is created as virtual (the easy fix)
>
> - change the behavior of virtual fields in order to really allow update of
> selected features only. This would probably imply that we have to store the
> primary keys of the selected features somewhere and can lead to follow-up
> problems later on.
>
> Any opinions on this?
>
> Personally I would say that virtual fields cannot update "selected only
> features" and disable that checkbox as soon as virtual fields are created.
>
> Andreas
>
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