QGIS – Creating QgsFeature with Default Attributes Using PyQGIS

default valuefields-attributespostgispyqgisqgis

I have a polygon layer loaded from PostGIS database. This layer has a default value for the first column. I can create a new feature set that attribute to some predefined value with:

newFeature = QgsFeature()
newFeature.setFields(activeLayer.pendingFields())
newFeature.setAttribute(0, "someValue")

But I want to set it to the default value that comes from the layer. When I try to add a feature with QGIS 2.10 it automatically sets the default value for that column. How can I achieve that with PyQGIS?

Best Answer

Default values are accessible via the data provider, so this may work for simple cases:

provider = activeLayer.dataProvider()
newFeature.setAttribute(0, provider.defaultValue(0))

QGIS 3

Select the layer in the layer panel and left-click. Select properties. Select the "Attributes Form" as shown below. Select the fields from the "Available Widgets" list as show. Provide an expression for the default value in the "Defaults" dialog. If the "Apply default value on update" is checked, the value will be adjusted every time the feature's geometry or another attribute is changed. This makes things like a "last_modified" timestamp or an updated "area" possible.

QGIS 2.18

Starting from QGIS 2.18 this is possible without any extra tools.

Just go to the field properties click on the button in the field you would like to assign a default value and enter an expression. It can also take the geometry as input.

Sidenote: I know that the original question targets QGIS 2.14, but I think this is still of interest to future readers of this question.

PyQGIS Attribute Inheritance – Creating New Layer with All Attributes Inherited from Original Layer Using PyQGIS

I reviewed your code and added just a few lines:

add the source fields to the centroids layer (addition 1)

The QgsVectorLayer class contains the fields() and updateFields() methods.

The QgsVectorDataProvider class has the addAttributes() method.
copy the source feature attributes to the new feature (addition 2)

The QgsFeature class possesses the setAttributes() method.

Here the complete working code :

layer = iface.activeLayer()

vl = QgsVectorLayer("Point?crs={}&index=yes".format(layer.crs().authid()), "centroids", "memory")
provider = vl.dataProvider()

### addition 1
provider.addAttributes(layer.fields())
vl.updateFields()
###

for feat in layer.getFeatures():
    new_geom = feat.geometry().centroid()
    new_feat = QgsFeature()
    new_feat.setGeometry(new_geom)
    ### addition 2
    new_feat.setAttributes(feat.attributes())
    ###
    provider.addFeature(new_feat)

QgsProject.instance().addMapLayer(vl)

The code above will result into:

References:

Getting field names of layer using PyQGIS

Best Answer

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