[QGIS-Developer] Updating a layer's datasource in python

[Denis Rouzaud]

Hi Olivier,

I have been playing with this and I think you should use the source on the
layer and not on the data provider.
Here is some code (which also modifies the style of the layer)
https://github.com/QGEP/customizer/blob/master/customizer.py#L129-L141

I was doing a layer.reload() after changing the source.

Hope that helps,
Denis

Le mar. 25 sept. 2018 à 19:02, Olivier Dalang <olivier.dalang at gmail.com> a
écrit :

> Dear List,
>
> As simple as it sounds, I'm struggling with changing the datasource of
> layers with python :
>
> layer1 = QgsVectorLayer('/path/to/a.shp')
> QgsProject.instance().addMapLayer(layer1)
> layer1.dataProvider().setDataSourceUri('/path/to/b.shp')
>
> The layer successfully changes on map redraw. However layer1.source()
> stays to the initial layer, so that the change does not persist across
> saves (save and reload, and you get a.shp again).
>
> The exact same code with a geopackage doesn't work at all (no changes on
> map redraw).
>
> layer1 = QgsVectorLayer('/path/to/db.gpkg|layer=a')
> QgsProject.instance().addMapLayer(layer1)
> layer1.dataProvider().setDataSourceUri ('/path/to/db.gpkg|layer=b')
>
> There is also an entry in the pyqgis cookbook (here
> <https://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/loadlayer.html#id1>,
> scroll down) for QgsVectorLayer. The layer1.source() is correctly updated,
> but again, it works with shapefiles, but not geopackages. And this is for
> vectors only.
>
> layer1.setDataSource('/path/to/b.shp', "b", "ogr")
>
> Am I hitting a bug ? Or did I get confused somewhere ?
>
> As I feel this is a fairly common need, I'd be very grateful if someone
> could help me figure out the recommended way to achieve this, for both
> vectors or rasters. I'll update the pyqgis cookbook in return :-)
>
> Note that there are workarounds (like replacing with a new layer and
> copying styles over or writing directly to the .qgs file, but they are not
> straightforward and have limitations).
>
> Thanks !!
>
> Olivier
>
>
>
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-- 

Denis Rouzaud
denis at opengis.ch  <denis at opengis.ch>
+41 76 370 21 22
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