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

[Raymond Nijssen]

Thanks Nyall, will try this today!

Raymond



On 05-12-2022 00:53, Nyall Dawson wrote:
> 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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