Update feature attributes in QGIS Plugin: 2 methods work in console but not in plugin

Question

The following code works to change and save the specified attribute of a selected feature in the QGIS console:

selectedLayer = iface.activeLayer() # add self before iface for external script
features = layer.selectedFeatures() # creates a list of features so you need to index it to access the feature
feature = features[0]
newValue1 = 'hello'
newValue2 = 'hola'
 
with edit(selectedLayer): # the with edit & update feature method works fine in Qgis console.
 feature.setAttribute('December', newValue1) # Tested with plain text instead of newValue1. Tested with feature['December'] = 'K'.
 feature.setAttribute('February', newValue2) # feel like it's something to do with how the target feature is specified and passed to the function.
 selectedLayer.updateFeature(feature)# Tested with commitChanges().
 print(feature.attributes())

However, the with edit statement does not work when applied in a plugin. The function is correctly called when the relevant button is pressed in the UI. Does with edit just not work in a plugin environment?

This is the code:

def saveFeatureEdits(self):
 print('Save Feature Edits called') # Prints so feature is called.
 global selectedLayer # Have tried with this in the function & also tried without; it works to get the selected feature so assume this isn't the problem.
 selectedFeature = selectedLayer.selectedFeatures()
 feature = selectedFeature[0]
 featureID = str(feature['ID'])
 print(featureID) # Prints the correct ID.
 newValue1 = self.dockwidget.editFeatureAttribute1.text()
 print(newValue1) # Prints the correct value.
 newValue2 = self.dockwidget.editFeatureAttribute2.text()
 print(newValue2) # Prints the correct value.
 with edit(selectedLayer): # the with edit & update feature method works fine in Qgis console.
 feature.setAttribute('December', newValue1)
 print(feature.attributes()) # Doesn't print anything.
 feature.setAttribute('February', newValue2)
 selectedLayer.updateFeature(feature) # Tested with commitChanges() and also with adding commitChanges() at the end.
 print(feature.attributes()) # Doesn't print anything.

Note that I've also tried the following in the QGIS console as an alternative. It works to update the attribute December to 'G' but only if I run the code twice, so as expected it doesn't work in the plugin. I am at a loss for how to update the feature attribute now in the plugin:

layer = iface.activeLayer() 
feature = layer.selectedFeatures() 
feature = feature[0] # access the feature
layerFields = layer.fields()
fieldIndex = layerFields.indexFromName("December")
feature = layer.selectedFeatures() # creates a list of features so you need to index it to access the feature
featureID = feature[0].id()
label = 'G'
layer.startEditing()
layer.changeAttributeValue(featureID, fieldIndex, label)
layer.commitChanges()
print(fieldIndex)
for f in feature:
 print(f.attributes())

Output in console 1st and 2nd run:

exec(open('...'.encode('utf-8')).read())
3
[10, 11182833, NULL, 'S']
exec(open('....encode('utf-8')).read())
3
[10, 11182833, NULL, 'G']
 

Answer 1

In the last code block, you change the value of the feature in the source data, not the value of the variable feature. So feature still remains unchanged.

At the first run, it prints the first/unchanged values of feature. At the second run, feature is assigned the changed values of the source data.

If you add feature = layer.selectedFeatures() before for loop, you will see that the attribute values have actually changed at the first run.

feature = layer.selectedFeatures()
for f in feature:
 print(f.attributes())

I couldn't test the issue in with edit.

• TuftyPuff: Thank you, the last code block now works correctly in the QGIS console. However it does not work when transferred to the plugin, so I will leave the question open for further comments.