[QGIS-Developer] Backward compatibility for style in project files between QGIS versions

Wed May 3 01:33:25 PDT 2023

This PR was about the symbology, but we noticed there are many other parts
of the QGS file which are not backward compatible.
If I'm not wrong :
- a WMS shortname on a group made with QGIS 3.20 can not be read with QGIS
3.18.
- field server configuration made with QGIS 3.16 can not be read with QGIS
3.14
- ...

These settings, (which are way older in the QGIS development, i.e already
present in QGIS 2), are just lost when read with a lower version of QGIS.
And obviously, all new features, options, checkbox etc are lost as well.

I understand, it's not easy to migrate a lot of softwares and to follow all
their versions in a big organization.
But using a QGIS recent version to write a file and then ask a lower
version QGIS to read is, anyway, leading to some reading issues I would
say. The PR was indeed trying to keep some backward compatibility about
symbology, which was nice, but there are other settings which are lost
already, so I would be careful with other settings in general ;-)

Just for your information, but I noticed these other settings as well ;-)

Le mar. 2 mai 2023 à 09:38, FERRATON Alain (Adjoint au chef de groupe) -
SG/DNUM/MSP/DS/GSG via QGIS-Developer <qgis-developer at lists.osgeo.org> a
écrit :

> Hi Denis,
>
> Thanks for your feedback.
>
> I think that re-introducing backwards compatibility in QGIS 3.28 would be
> valuable for our services. The size of the project files is not too
> critical in my opinion compared to the size of the data files, which are
> usually much larger.
>
> Is this possible for QGIS 3.28.7?
>
> Alain
> ---
>
> *Alain FERRATON*
> Adjoint au chef de groupe
> MSP/DS/GSG
> Direction du numérique | Secrétariat général
>
> MAN 7, rue René Viviani 44200 NANTES
> Bureau : MAN étage 1 plateau B
> Tel : +33 240128408 - Mobile : +33 671794593
> www.ecologie.gouv.fr
> [image: Marianne] Secrétariat général
> MINISTÈRES
> TRANSITION ÉCOLOGIQUE
> COHÉSION DES TERRITOIRES
> TRANSITION ÉNERGÉTIQUE
> MER
> [image: liberté, égalité, fraternité]
>
>
> Le 28/04/2023 10:02, > denis.rouzaud a écrit :
>
> Hi Alain,
>
> Yes, the backward compatibility to 3.16 has been removed in 3.28,
> considering there was a LTR in between and that 3.16 was not maintained for
> more than a year.
>
> The PR is here https://github.com/qgis/QGIS/pull/45143
>
> I am not sure if it's possible to do it with a plugin.
> An approach would be to revert this in the 3.28 branch to give more time.
> I have no strong opinion here. The main motivation to drop compatibility
> was the size of the project file and redundancy of information (manually
> editing the file gets harder).
>
> Denis
>
>
> Le jeu. 27 avr. 2023, 09:08, FERRATON Alain (Adjoint au chef de groupe) -
> SG/DNUM/MSP/DS/GSG via QGIS-Developer <qgis-developer at lists.osgeo.org> a
> écrit :
>
>> Hi
>>
>> A polygon layer saved in a project file with QGIS 3.28 is systematically
>> opened in blue in QGIS 3.16 (the style is lost).
>>
>> There has been a change in the storage of style in project files
>> introduced in QGIS 3.22.
>>
>> QGIS 3.22 save the style in both formats (<Option.../>
>>
>> and <prop k=.../>
>>
>> (see the attachment)
>>
>> This is no longer the case in QGIS 3.28
>>
>> We have a heterogeneous QGIS version park. The non backward compatibility
>> of style is an important brake to migrate progressively our services to
>> QGIS 3.28
>>
>> We could consider developing or having developed a plugin to ensure this
>> backward compatibility.
>> Is this possible? What would be the best way to proceed? Can we find
>> documentation on the storage of styles in QGIS project files and on its
>> evolution?
>> (I didn't find anything relevant by searching on the internet).
>>
>> Sincerely,
>> --
>>
>> *Alain FERRATON*
>> Adjoint au chef de groupe
>> MSP/DS/GSG
>> Direction du numérique | Secrétariat général
>>
>> MAN 7, rue René Viviani 44200 NANTES
>> Bureau : MAN étage 1 plateau B
>> Tel : +33 240128408 - Mobile : +33 671794593
>> www.ecologie.gouv.fr
>> [image: Marianne] Secrétariat général
>> MINISTÈRES
>> TRANSITION ÉCOLOGIQUE
>> COHÉSION DES TERRITOIRES
>> TRANSITION ÉNERGÉTIQUE
>> MER
>> [image: liberté, égalité, fraternité]
>> _______________________________________________
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>
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