QGIS' virtual fields (expression fields) are not
https://www.postgresql.org/docs/current/ddl-generated-columns.html
They are conceptually similar between QGIS and PostgreSQL, but they are
not propagated from QGIS to the data source as a new column there. They
live only in the QGIS project.
If you want a generated column in your PostgreSQL database, you need to
add it another way. E.g. via an SQL query.
Cheers, Hannes
On 26.07.24 12:46, Roland Berger via QGIS-User wrote:
Hi
I would like to add a virtual field to a PostGIS vector layer with
PyQGIS with standalone scripts
(https://docs.qgis.org/3.34/en/docs/pyqgis_developer_cookbook/intro.html#python-applications)
All examples I have found so far with google, chatgpt4 and JetBrains
AI Assistant gave me solutions that do not work. They only work in the
Python Console inside QGIS.
Does anybody know of a solution that works with PyQGIS with standalone
scripts?
See below what I have tried so far in different variations.
Thanks for any help
Roland
Example created by chatgpt:
...
field_name = "virtual_field"
expression = '"attribute_name" * 2' # Example expression
# Create and add the virtual field
layer.startEditing()
layer.addExpressionField(expression, QgsField(field_name, QVariant.Double))
layer.commitChanges()
...
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