[QGIS-Developer] QGIS expression based layer filters

[Carlo A. Bertelli (Charta s.r.l.)]

Very interesting indeed.
When I worked with Mapinfo, maybe 40 years ago, I remember using the
"MapBasic" window to build query-generated layers.
I think it would be very handy and substitute generating lots of geometric
views inside the database (what a mess!).
As Alessandro says, there are drawbacks in any solution, but operating the
query inside the database (storing the query as a sort of "local view") is
really much more efficient and does not require duplicating the backend via
Spatialite with a lot of network traffic and cache size (see what happens
with joins made at the client level in Properties).
Meanwhile, the Query Builder is much more convenient and using the same
syntax all the time is a good idea, but it could be optional, letting the
user decide what to do.
Anyway, this means creating "automatic temporary tables"; reducing them to
filters only means missing some opportunities.
I think we must make an effort to define use cases in a more rigorous way.
I see a fuzzy scenario with possible misunderstanding between geodatabase
parlance and GIS concepts, between application structure and use cases.
Maybe it's only fog inside my mind, but the long gestation about the Query
Builder suggests that I am not alone.
Thanks for keeping reasoning on these issues.
c


On Wed, Sep 24, 2025 at 8:54 PM Nyall Dawson via QGIS-Developer <
qgis-developer at lists.osgeo.org> wrote:

>
>
> On Wed, 24 Sept 2025, 10:56 pm David Signer via QGIS-Developer, <
> qgis-developer at lists.osgeo.org> wrote:
>
>> Hi there
>>
>> I've been considering enhancing the Query Builder (accessible via Layer
>> -> Filter...) by QGIS expression based filters. At least with project and
>> global scope.
>> Maybe with tabs to distinguish between "provider side filter" (current
>> functionality) and "expression filter" (new functionality).
>>
>> Any opinions on this? In my view, this could be valuable because it's
>> available on all kinds of data-layers and allows us to use variables and
>> functions for filtering as well.
>>
>
> Can you make sure you file a QEP before starting any work? 👍
>
> Nyall
>
>>
>> Thanks for any feedback and cheers
>> Dave
>>
>> --
>>
>> Dave Signer
>> Senior Developer & INTERLIS Architect
>> OPENGIS.ch - Team QGIS & Industry Solutions
>>
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