[QGIS-Developer] Questions wrt. problems with empty layers

[Lars I. Nielsen, LIFA A/S]

Hi developers.

I asked this question on the user's list, so far without any answers, but have been advised to ask here as well.


I'm working with a number of projects, which statically open a fixed number of layers. All layers are fetched using WFS / WFS-T.

Each layer has an extensive rule based styling, and an extensive field/attribute dialog setup. This is saved in the project files.

Our plugin changes the data provider filter for many layers, when the user works with the data. These filter expressions are also saved in the project, of course.

Our problem is, that if the user accidently chooses a work area (= new data provider filter), which contain no data in any layer, those layers lose all styling etc. And it's apparently impossible to recover these styles etc. by changing the filter back.

So basically the user's project is unrecoverably trashed at this point in time.

A - Is this a correct description of how QGIS handles "no-data" layers ?

B - Are there any standard ways to handle this in QGIS (using metadata or otherwise) in an automated fashion (i.e. not manually) ?

C - If the answers to A and B are yes and no resp., are there any plans to remedy this unnecessarily serious problem ?


Might it not be solved simply by adding an (optional?) layer metadata key, that stores the last used topology, and revert to this if no data are found on the layer ?


Using 3.4.5 x64 (Danish)


Med venlig hilsen
Lars I. Nielsen, LIFA A/S
GIS-konsulent, FME Certified Professional

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