Create layer using selected features from WFS layer using PyQGIS

Question

I am making a plugin that loads a WFS layer and lets the user filter out the information they need and create a layer based on that filtering. The new layer is created from the original layer based on expressions that are created from the users filtering. This prosess can be very slow as the WFS layer is rather large. I would therfore like to know if there is any faster or betther ways of doing this.

Here is an example of my code:

expr_string = "\"kommune\"=301 AND \"funksjon\"='kultur'" #example of an expr_string
expr = QgsExpression(expr_string)
it = vlayer.getFeatures( QgsFeatureRequest( expr ) )
ids = [i.id() for i in it]
vlayer.setSelectedFeatures( ids )
selectedFeatures = vlayer.selectedFeatures()
tempLayer = QgsVectorLayer("Point?crs=epsg:4326", "newLayer", "memory")
QgsMapLayerRegistry.instance().addMapLayer(tempLayer)
temp_data = tempLayer.dataProvider()
attr = vlayer.dataProvider().fields().toList()
temp_data.addAttributes(attr)
tempLayer.updateFields()
temp_data.addFeatures(selectedFeatures)

This code is based on an anwer from this post: Quickly make server side spatial filters for WFS layers based on other layer's selected geometries in QGIS

• LaughU: did you check where the bottleneck is? adding a print datetime.datetime.now().time() after every major step might give you an impression where your efforts are needed
• Kasper Skjeggestad: @Joseph thx, I have tried it now, it seems that it is selectedFeatures = vlayer.selectedFeatures() is the onw that took the most time.

Answer 1

You could try using virtual layers instead of memory layers. Note that I can't confirm if this is faster than your method as I don't know how large your WFS layer is:

layer_name = vlayer.name()
query = "SELECT * FROM " + layer_name + " WHERE kommune = '301' AND funksjon = 'kultur'"
vLayer = QgsVectorLayer("?query={}".format(query), "Output", "virtual" )
QgsMapLayerRegistry.instance().addMapLayer(vLayer)

• Kasper Skjeggestad: This seems to work quite well, thanks. Do you however know if this is possible to do this without adding the original layer to the layers panel (canvas?)?
• Joseph: @KasperSkjeggestad - Most welcome! It may be possible but I haven't found a way to do it unfortunately...