Hi Yves,
why does the featureId not point to the PK? Can you guarantee that the
value is unique in the view? Maybe it is not?
Another thought: I normally use QgsVectorLayer.setSubsetString() to
reduce the amount of features being loaded into QGIS in the first place
(and by using the subsetString I let PG deal with it). Thus I can use
plain SQL and do not have to fuzz with QgsFeatureRequest.
hope this helps
Bernhard
Am 09.12.2015 um 18:36 schrieb Yves Moisan:
Hi All,
Sorry for X-posting. I originally put this message on the qgis-dev list
but I guess it wasn't the right place.
I'm contributing to a QGIS python plugin. Dev environment : 2.8.3
(compiled) Ubuntu 14.04.
I have an issue getting a list of PK ids from selected features on a
vector layer pointing to a PG view . The short story is : I would like
to use selectedFeaturesIds() but I can't rely on ids returned being the
actual PK. The longer story now.
I can use QGSFeature objects and get the field I want. However, all
variants that give a list of QGSFeature objects that I've tried fail
given a large enough number of selected features :
# getting all features with attributes and geom; definitely overkill
layer_selected_features = layer.selectedFeatures() # Then extract the
attribute I want
# getting all features but only with the (predetermined) table_pk;
layer_selected_features_ids was obtained by selectedFeaturesIds()
layer.getFeatures(QgsFeatureRequest().setFilterFids(layer_selected_features_ids).setFlags(
QgsFeatureRequest.NoGeometry ).setSubsetOfAttributes(
[table_pk],layer.pendingFields() ))) # Then extract the attribute I want
A note on the previous line : I found out order of the filtering
elements matters.
# Using a feature iterator
layerSelectedFeaturesIterator = layer.selectedFeaturesIterator()
layer_selected_features_ids = list(i[table_pk] for i in
layerSelectedFeaturesIterator) # I get directly the list of items I want
When the feature selection gets large enough the code fails silently and
no list is returned.
I was hoping I could use selectedFeaturesIds(). I tried it with my
largest data sets and it works. Only problem is : the id list it
returns may or may not correspond with the actual table PK the view
points to. setKeyColumn() on the layer won't make selectedFeaturesIds()
return a list of ids with the new keyColumn(). I was thinking maybe I
could pass in the field name for the PK (that I know) to some
constructor (datasource, layer ?) and then be satisfied the list of ids
returned by selectedFeaturesIds() would be fine.
Pointers appreciated.
Cheers,
Yves
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