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

Wed May 3 01:53:44 PDT 2023

Hi Etienne, 

It is normal that backwards compatibility of projects is generally not
guaranteed. 

However, if it can be done with little effort, especially for highly
visible functionalities such as style, it can be an important advantage
to motivate our services to migrate to the latest LTR version in a
progressive manner (and thus with a temporarily heterogeneous version
park).

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 [1]

 		Secrétariat général

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TRANSITION ÉCOLOGIQUE
COHÉSION DES TERRITOIRES
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MER 

Le 03/05/2023 10:33, > etienne.trimaille a écrit :

> 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 [1]
> 
> Secrétariat général
> 
> MINISTÈRES
> TRANSITION ÉCOLOGIQUE
> COHÉSION DES TERRITOIRES
> TRANSITION ÉNERGÉTIQUE
> MER 
> 
> 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 [1]
> 
> Secrétariat général
> 
> MINISTÈRES
> TRANSITION ÉCOLOGIQUE
> COHÉSION DES TERRITOIRES
> TRANSITION ÉNERGÉTIQUE
> MER 
> 
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