How do I get a list of fields that have been joined to a layer, or how can I check if a specific field has been joined?
In older versions there seemed to be field.source(), but this is not available anymore.
I am not performing the join via PyQGIS. The join is done manually and I would just like to use PyQGIS to detect which fields have been joined.
One can detect which fields have been joined by means of the QgsFields class and its method fieldOrigin:
Returns the field's origin (value from an enumeration).
from qgis.core import QgsProject
layer = QgsProject.instance().mapLayersByName("points")[0]
joined_fields = []
if len(layer.vectorJoins()) > 0:
fields = layer.fields()
for field in fields:
field_name = field.name()
indx = fields.indexOf(field_name)
if fields.fieldOrigin(indx) == fields.OriginJoin:
# or if fields.fieldOrigin(indx) == 2:
joined_fields.append(field_name)
print(joined_fields)
The above code will result in a list of fields that have been joined to a layer. In my case it will be:
['month', 'month2', 'month3']
2 = OriginJoin means that this field comes from a joined layer.
OriginJoinField comes from a joined layer (originIndex / 1000 = index of the join, originIndex % 1000 = index within the join)
References: