[QGIS-Developer] [python] saveStyleToDatabase() bug when saving more than one layer to a GPKG

[Jésahel Benoist]

Hi ! I'm happy to join this list. Hope you can help with this nasty bug,
two days I'm on it...

Regards,

Jésahel

**Describe the bug**
For a plugin, I need a way to save my layers in a geopackage with their own
style, exactly like the "Package" Tool.
The problem arises when two or more layers are saved. In the destination
gpkg, the layer_styles table contains one row by layer, the styleName field
is OK but the f_table_name field contains another layer name. I'm almost
sure that the bug is in the saveStyleToDatabase() function. I've tried
everything, almost reproducing the [Package tool function](
https://github.com/qgis/QGIS/blob/master/src/analysis/processing/qgsalgorithmpackage.cpp
)

**How to Reproduce**
Create two layers with their own style named test and test 2 (or download
this one [
http://djes.free.fr/qgis/test.gpkg](http://djes.free.fr/qgis/test.gpkg)).
Adjust the script to the layers name and destination geopackage. Launch the
script for the first layer, destination file is OK. For the second, the
style is not correctly saved.

**QGIS and OS versions**
3.16.5 and 3.18.1 / Windows 10

Simplified code (or download it on
http://djes.free.fr/qgis/saveLayerWithStyle.py)
[code]
layer_name = 'test' #change me
gpkg_name = 'c:\\temp\\mytest.gpkg' #change me if needed

# First, saves the layer
src_layer = QgsProject.instance().mapLayersByName(layer_name)[0]
options = QgsVectorFileWriter.SaveVectorOptions()
options.actionOnExistingFile = QgsVectorFileWriter.CreateOrOverwriteLayer
options.layerName = layer_name
#options.SymbologyExport = QgsVectorFileWriter.FeatureSymbology
#options.driverName = "GPKG"
error = QgsVectorFileWriter.writeAsVectorFormatV2(src_layer, gpkg_name,
QgsProject.instance().transformContext(), options)

if error[0] == QgsVectorFileWriter.ErrCreateDataSource:
    print("Create mode")
    options.actionOnExistingFile =
QgsVectorFileWriter.CreateOrOverwriteFile #Create mode
    error = QgsVectorFileWriter.writeAsVectorFormatV2(src_layer, gpkg_name,
QgsProject.instance().transformContext(), options)
del options
if error[0] == QgsVectorFileWriter.NoError:
    print('Layer "' + layer_na

me + '" saved in "' + gpkg_name + '"')
else:
    print(error)
    raise Exception('Failed to save layer')

# Second, saves the style
# Load just saved layer
dst_layer = QgsVectorLayer(gpkg_name, layer_name)
if not dst_layer.isValid():
    raise Exception('Failed to load layer')
#print(dst_layer)

myDocument = QDomDocument('qgis')
src_layer.exportNamedStyle(myDocument)
#print(myDocument.toString())
success, message = dst_layer.importNamedStyle(myDocument)
dst_layer.saveStyleToDatabase(layer_name, '', True, '')
QgsProject.instance().removeMapLayer(dst_layer)
del src_layer
del dst_layer
del myDocument
[/code]
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