[QGIS-Developer] createvectorTable error: Could not retrieve driver for connection

[Nyall Dawson]

On Fri, 2 Dec 2022 at 23:05, Richard Duivenvoorde via QGIS-Developer
<qgis-developer at lists.osgeo.org> wrote:
>
> Ok, I think I found the crux!
>
> With your code QGIS 3.26 will CREATE a new geopackage... (if it is not there yet)
> After which QGIS master is fine
>
> BUT QGIS master apparently does NOT create a new geopackage with your code...
> So IF there is an excisting test.gpkg, all is fine
> IF there is not one, it depends on you QGIS version if it creates a fresh one or not?
>
> Maybe some core dev can say something about this?

I'd say the old behaviour was an unintentional bug, and that
createConnection should only be used with a path that already exists.

For 3.28 and later you can create empty databases using
QgsProviderMetadata.createDatabase(uri), eg:

QgsProviderRegistry.instance().providerMetadata('ogr').createDatabase('/path/to/data.gpkg')

After that you can create a connection to the db using createConnection safely.

Nyall



>
> Regards,
>
> Richard Duivenvoorde
>
> On 12/2/22 13:53, Richard Duivenvoorde via QGIS-Developer wrote:
> > Hi Raymond,
> >
> > I've updated your test script a little:
> >
> > gpkg_fn = '/tmp/test.gpkg'
> > try:
> >      print(QgsProviderRegistry.instance().providerList())
> >      md = QgsProviderRegistry.instance().providerMetadata('ogr')
> >      print(f'md = {md}')
> >      conn = md.createConnection(gpkg_fn, {})
> >      print(f'conn = {conn}')
> >      fields = QgsFields()
> >      fields.append(QgsField('key', QVariant.String))
> >      fields.append(QgsField('value', QVariant.String))
> >      conn.createVectorTable('', 'test', fields, QgsWkbTypes.NoGeometry, QgsCoordinateReferenceSystem(), True, {})
> > except Exception as e:
> >      print(f'ERROR: {e}')
> >
> > As said: in my freshly compiled master, this fails to run with 'Could not retrieve driver for connection'
> > It also fails on my 3.28.0 version I have in a Windows VM.
> >
> > It DOES print the 'ogr' driver in the providerList() though.
> >
> > Strange behaviour: after starting (the older compiled) Qgis 3.26 on the same Linux system (in 3.26 the script always seems to work...) QGIS master ALSO works!!!
> >
> > So I thought it had something todo with loading different provider registries or so?
> > Maybe master not having something but after starting 3.26 it was there?
> > Or is it loading (different) gdal/ogr libs order?
> > Did something change there?
> >
> > Looking that the createConnection docs:
> > https://qgis.org/pyqgis/master/core/QgsConnectionRegistry.html#qgis.core.QgsConnectionRegistry.createConnection
> > I thought to see that your 'id' was only the filename, but adding ogr:// in front of it does not even work...
> > So not sure if that createConnection doc is old, or if I'm looking in the wrong createConnection...
> >
> > Anybody can
> >
> >
> >>>
> > On 12/2/22 12:30, Raymond Nijssen via QGIS-Developer wrote:
> >> No one having a clue? Should I create an issue?
> >>
> >> Raymond
> >>
> >>
> >> On 30-11-2022 18:08, Raymond Nijssen via QGIS-Developer wrote:
> >>> Hi developers,
> >>>
> >>> Recently some users of my plugin started getting errors in the code that creates a .gpkg file with a table. I wrote a piece of test code:
> >>>
> >>> gpkg_fn = '/home/raymond/tmp/test.gpkg'
> >>> md = QgsProviderRegistry.instance().providerMetadata('ogr')
> >>> conn = md.createConnection(gpkg_fn, {})
> >>> fields = QgsFields()
> >>> fields.append(QgsField('key', QVariant.String))
> >>> fields.append(QgsField('value', QVariant.String))
> >>> conn.createVectorTable('', 'test', fields, QgsWkbTypes.NoGeometry, QgsCoordinateReferenceSystem(), True, {})
> >>>
> >>>
> >>> That last line *sometimes* results in this error:
> >>>
> >>> _core.QgsProviderConnectionException: Could not retrieve driver for connection
> >>>
> >>>
> >>>
> >>> I cannot reproduce the error on my laptop (Linux), but Richard tried a few QGIS versions in both Windows and Linux and *sometimes* got the error and sometimes not. Even in the same application, the error disappeared after running another version of QGIS simultaneously... :/
> >>>
> >>> No clue if this error is GDAL or Qt or whatever related, pretty puzzling for me. Hope anyone can help!
> >>>
> >>> Kind regards,
> >>> Raymond
> >>> _______________________________________________
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