QGIS » QGIS Application

Not sure if this is a regression or something which was never supported, but virtual layers always return the same feature when attempting to fetch a particular feature with a filterfid request.

Steps to reproduce:

1. load two layers
2. create a virtual layer using a cross join type "select * from layerA, layerB"
3. Try fetching features using a non restricted request, eg:

ids = [f.id() for f in layer.getFeatures()]

this works OK
4. Try fetching a specific feature:

f.getFeatures(QgsFeatureRequest.setFilterFid(ids[4])).next()

Regardless of the feature id requested, only the first feature in the table is returned.

This may be due to the query not having a unique key field - but if that's the case it becomes impossible to create cross join type virtual layers (since sqllite doesn't have a row_number() type function which could be used to create fake unique ids in the query).

This breaks various QGIS functionality with the resultant layer - e.g. it can't be used with atlas. Possibly #15709 is related too.