[QGIS-Developer] Drill-down (cascading) forms in QGIS Value Relation Widgets crowdfunding

[Matthias Kuhn]

Hi Alessandro,

Thanks a lot for these detailed insights!

On 04/17/2018 12:44 PM, Alessandro Pasotti wrote:
> Hi,
>
> I'll try to address all concerns in a single mail (what a challenge!)
>
> First I would like to say that everybody has access to a different set
> of "average/typical users" and I cannot claim any statistical
> relevance to the group of users I've been in touch with.
>
> But the user's feedback that I've got so far is that the
> Value-Relation widget (V-RW) is easier to use and to understand: its
> scope it's limited to how data are entered and viewed and does not
> depend on a model-project-level constraint (the Relation-Reference
> R-RW does).
>
> Those (statistically insignificant) users were quite emotional and
> ready to fight to keep V-RW live and healthy :)

May they be statistically significant or not, the opinion counts and is
important to be considered. I assume, the main requirement here is an
easy setup (i.e. directly in the widget, no roundtrip via project
properties). As long as this is not implemented, the value relation
widget will stay alive.

Let's focus on what other requirements are potential show-stoppers and
then decide if it's worth moving on.

> Code-wise I totally agree that the two widgets could share more logic
> and options, but given the intricacies of the attr-table and
> widgets-forms logic this is not trivial at all, and it's not in scope
> with this QEP 116 enhancement.
>
> Coming to the new functionalities introduced by QEP 116, the way they
> will be implemented will make them easily reusable in the context of
> the R-RW:
>
> - form scope context with geometry and attributes
> - form scope available in both the form and the attribute table

And that's what I really like about it!

>
> Of course existing bugs and glitches in the V-RW workflow will be
> fixed on the way when they not imply rewriting the whole QGIS core ;)
>
> What could be considered here, is to add a second goal to the campaign
> for making the new features available to the R-RW too, what do you think?

As written in my previous email, please do !!

>
> But even without this additional goal, I still think that this QEP
> (which is not a complete refactoring of the whole form/attr-table *-R
> widgets) is a step forward and in the direction of a future better
> integration of the existing *-R-widgets.
>
>
> That's why I'm joining Nyall's call to contribute and make this a reality.
>
>
> Also note that some of Règis requirements, like a geographical dynamic
> filter will be possible with an expression like:
>
> ... AND contains(buffer( $current_form_geometry, 10), $geometry)

... and even better with the R-R widget where it will be possible to
dynamically adjust the range from the form (thinking of advanced search
functionality in a popup or so), its new infrastructure allows for some
very cool additions which I hope to be able to implement soon ;)

Please keep up the good work and let us know what's required to bring
this to relation reference too!

Best regards
Matthias

> note that this expression is the one used to filter the values in the
> related layer, and it will have access to the geometry of the feature
> currently being edited/added in the form (or table row) as well as to
> the form (row) values, so:
>
> - $current_form_geometry = the geometry of the feature currently being
> edited in the form
> - $geometry = the geometry of the related layer that is being filtered
> to get the list of values for the combo/search/etc...
>
> Also note that the V-RW is already used in the identify results panel
> (and form of course).
>
>
> Cheers
>
> -- 
> Alessandro Pasotti
> w3:   www.itopen.it <http://www.itopen.it>
>
>
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-- 
Matthias Kuhn
matthias at opengis.ch <mailto:matthias at opengis.ch>
+41 (0)76 435 67 63 <tel:+41764356763>
OPENGIS.ch Logo <http://www.opengis.ch>
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