I'm trying to edit the value of an attribute for each feature in a layer using a QGIS Python plugin. I've found that doing this outside of editing mode is much slower than while editing (even including committing the edits). See code below (lines interchangeable at the same point in a loop). The difference in speed for my sample dataset is 2 seconds (edit mode) vs 72 seconds (not edit mode).
Modifying an attribute in edit mode:
layer.changeAttributeValue(feature.id(), 17, QtCore.QVariant(value))Modifying an attribute outside of edit mode:
layer.dataProvider().changeAttributeValues({ feature.id() : { 17 : QtCore.QVariant(value) } })Is this an expected behavior? I don't need the user to be able to undo the changes, so I don't think I need to use edit mode.
Edit 1: See full code below with both versions included (but commented out):
def run(self): try: # create spatial index of buffered layer index = QgsSpatialIndex() self.layer_buffered.select() for feature in self.layer_buffered: index.insertFeature(feature) # enable editing #was_editing = self.layer_target.isEditable() #if was_editing is False: # self.layer_target.startEditing() # check intersections self.layer_target.select() self.feature_count = self.layer_target.featureCount() for feature in self.layer_target: distance_min = None fids = index.intersects(feature.geometry().boundingBox()) for fid in fids: # feature's bounding box and buffer bounding box intersect feature_buffered = QgsFeature() self.layer_buffered.featureAtId(fid, feature_buffered) if feature.geometry().intersects(feature_buffered.geometry()): # feature intersects buffer attrs = feature_buffered.attributeMap() distance = attrs[0].toPyObject() if distance_min is None or distance < distance_min: distance_min = distance if self.abort is True: break if self.abort is True: break # update feature's distance attribute self.layer_target.dataProvider().changeAttributeValues({feature.id(): {self.field_index: QtCore.QVariant(distance_min)}}) #self.layer_target.changeAttributeValue(feature.id(), self.field_index, QtCore.QVariant(distance_min)) self.calculate_progress() # disable editing #if was_editing is False: # self.layer_target.commitChanges() except: import traceback self.error.emit(traceback.format_exc()) self.progress.emit(100) self.finished.emit(self.abort)Both methods produce the same result, but writing via the data provider takes much longer. The function classifies proximity of building features to nearby fields (purple) using pre-created buffers (brown-ish).
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Modifying an attribute in edit mode:
layer.changeAttributeValue(feature.id(), 17, QtCore.QVariant(value))Modifying an attribute outside of edit mode:
layer.dataProvider().changeAttributeValues({ feature.id() : { 17 : QtCore.QVariant(value) } })Is this an expected behavior? I don't need the user to be able to undo the changes, so I don't think I need to use edit mode.
Edit 1: See full code below with both versions included (but commented out):
def run(self): try: # create spatial index of buffered layer index = QgsSpatialIndex() self.layer_buffered.select() for feature in self.layer_buffered: index.insertFeature(feature) # enable editing #was_editing = self.layer_target.isEditable() #if was_editing is False: # self.layer_target.startEditing() # check intersections self.layer_target.select() self.feature_count = self.layer_target.featureCount() for feature in self.layer_target: distance_min = None fids = index.intersects(feature.geometry().boundingBox()) for fid in fids: # feature's bounding box and buffer bounding box intersect feature_buffered = QgsFeature() self.layer_buffered.featureAtId(fid, feature_buffered) if feature.geometry().intersects(feature_buffered.geometry()): # feature intersects buffer attrs = feature_buffered.attributeMap() distance = attrs[0].toPyObject() if distance_min is None or distance < distance_min: distance_min = distance if self.abort is True: break if self.abort is True: break # update feature's distance attribute self.layer_target.dataProvider().changeAttributeValues({feature.id(): {self.field_index: QtCore.QVariant(distance_min)}}) #self.layer_target.changeAttributeValue(feature.id(), self.field_index, QtCore.QVariant(distance_min)) self.calculate_progress() # disable editing #if was_editing is False: # self.layer_target.commitChanges() except: import traceback self.error.emit(traceback.format_exc()) self.progress.emit(100) self.finished.emit(self.abort)Both methods produce the same result, but writing via the data provider takes much longer. The function classifies proximity of building features to nearby fields (purple) using pre-created buffers (brown-ish).
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