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

2018-09-25 Thread 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  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
> ,
> 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
de...@opengis.ch  
+41 76 370 21 22
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Re: [QGIS-Developer] Updating a layer's datasource in python

2018-09-25 Thread Nyall Dawson 
On Wed, 26 Sep 2018 at 09:02, Olivier Dalang  wrote:
>
> 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')

This code won't work correctly -- you shouldn't be changing the data
source of the layer's provider, but rather set the layer's data source
and let it handle the required changes to the provider.

> There is also an entry in the pyqgis cookbook (here, 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.

This should work for geopackage (as well as shp). Can you share your code?

And yes, there's unfortunately no equivalent for rasters yet.

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

2018-09-25 Thread Olivier Dalang 
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
,
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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