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I have a function that uses a layer already styled using another function and saves it as a .gpkg and I want to save the style in that .gpkg:

def saving_gpkg(styled_layer):
    options = QgsVectorFileWriter.SaveVectorOptions()
    options.driverName = "GPKG"
    QgsVectorFileWriter.writeAsVectorFormatV2(styled_layer, "nice_filename", QgsCoordinateTransformContext(), options)
    styled_layer.saveStyleToDatabase("polygon", "style automatically created", True, "")

The .gpkg is created, but if I open the created file, it doesn't have the defined style, just a random single symbol. I'm missing something?

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3 Answers 3

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10

A working example based on your code. Be aware that my code scope is limited as I use a layer name without space for everything whereas I should sanitized it in particular for layername parameter reused in the GPKG. Most of the code logic is based on qgsalgorithmpackage.cpp C++ code used in Processing algorithm "Package layers" in the answer from @leo-cardona

# Import required if not present
from qgis.PyQt.QtXml import QDomDocument
from qgis.core import (QgsReadWriteContext, QgsProject,
                       QgsVectorFileWriter, QgsVectorLayer)

def saving_gpkg(styled_layer, out_path):
    context = QgsProject.instance().transformContext()
    name = styled_layer.name()
    options = QgsVectorFileWriter.SaveVectorOptions()
    options.layerName = name
    options.fileEncoding = styled_layer.dataProvider().encoding()
    options.driverName = "GPKG"
    QgsVectorFileWriter.writeAsVectorFormatV2(styled_layer, out_path, context, options)
    doc = QDomDocument();
    readWriteContext = context = QgsReadWriteContext()
    styled_layer.exportNamedStyle(doc);
    gpkg_layer = QgsVectorLayer(f"{out_path}|layername={name}", name, "ogr")
    gpkg_layer.importNamedStyle(doc)
    gpkg_layer.saveStyleToDatabase(name, "", True, "")
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  • I can confirm this works Using QGIS 3.16.6 :-), the only thing I needed to do was to import those extra functions: from qgis.PyQt.QtXml import QDomDocument, from qgis.core import QgsReadWriteContext and just a few renames like the input layer object and the output path. FYI my layers/datasets are in Postgres and my styles are also saved in Postgres.
    – GIS_py
    Aug 2, 2021 at 13:38
  • Edited to add all required import
    – ThomasG77
    Aug 2, 2021 at 14:18
  • 1
    The function above only seems to save the active style. Any idea how you could adapt this for multiple styles ? I sometimes have multiple styles applied to the same layer (saved in a postgres DB).
    – lhowarth
    Apr 15, 2022 at 13:43
8

If you want to save one or several layers in a geopackage, the easiest way is to use the package algorithm which has the SAVE_STYLES parameter which must be True if you want to save the styles that your layers have in the geopackage that will be generated.

filename = '/home/ai/Desktop/prueba.gpkg'
layers = [styled_layer]
processing.run("native:package", {'LAYERS': layers, 'OUTPUT': filename, 'OVERWRITE': False, 'SAVE_STYLES': True})
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1

I developed a plugin that saves all styles with each layer as a .gpkg. Published on the official QGIS plugin repo: https://plugins.qgis.org/plugins/SaveAllScript/

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2
  • 1
    This is not answering the question. The Q is about programming.
    – Kadir Şahbaz
    Jun 30 at 8:08
  • I would like to clarify that this comment is relevant to the question because I created a QGIS plug-in that addresses some of the questions that the original poster had. I am sharing it here because maybe people in the future who also share the same questions can easily fix their problem with the plug-in. People are welcome to reference the code for the plug-in in order to help them with their own programming goals.
    – CaptainDang
    Jun 30 at 23:17

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