Rotating features in memory layer using PyQGIS

Question

I can rotate polygon features in a shapefile using:

vlayer = iface.activeLayer()
vlayer.startEditing()
for ft in vlayer.getFeatures():
    geom = ft.geometry()
    pt = ft.geometry().centroid().asPoint()
    geom.rotate(45, pt)
    vlayer.dataProvider().changeGeometryValues({ 0 : geom })

vlayer.commitChanges()

But if I use this on a memory layer, nothing happens. True values are printed on the console but the features are not rotated, even after refreshing the canvas and repainting the layer.

Is there a way to do this for memory layers?

Answer 1

A recipe for your intent (deduced from answer Qgis 2.7 (Dev) feature rotation?)

rotation = 45
vlayer = iface.activeLayer()
provider = vlayer.dataProvider()

couples_id_geom = []
for feature in vlayer.getFeatures():
    geom = feature.geometry()
    centroid = feature.geometry().centroid().asPoint()
    geom.rotate(rotation, centroid)
    # accumulate args to avoid rotation feature by feature
    couples_id_geom.append([feature.id(), geom])

# Change the layer features rotation in one go
provider.changeGeometryValues({
  couple_id_geom[0]: couple_id_geom[1] for couple_id_geom in couples_id_geom
})

# Refresh to see the changes
vlayer.triggerRepaint()