Creating Virtual Layer with PyQGIS

Question

Is it possible to create a Virtual Layer through a Python script?

For example, I have a layer 'road', and I would like to perform the SQL query:

SELECT *
FROM road
WHERE type = 'Expressway'

Will this be possible? Is there any example I can refer to?

Answer 1

For QGIS 3, instead use QgsProject:

from qgis.core import QgsVectorLayer, QgsProject
sql_query = "SELECT * FROM road WHERE type = 'Expressway'"
vlayer = QgsVectorLayer(f"?query={sql_query}", "vlayer", "virtual")
QgsProject.instance().addMapLayer(vlayer)

• sigeal: Given current LTR QGIS version is 3.10, this answer should be the new validated one !

Answer 2

For QGIS 2 you could use something like the following:

from qgis.core import QgsVectorLayer, QgsMapLayerRegistry
sql_query = "SELECT * FROM road WHERE type = 'Expressway'"
vlayer = QgsVectorLayer(f"?query={sql_query}", "vlayer", "virtual")
QgsMapLayerRegistry.instance().addMapLayer(vlayer)

You can find examples on how to use virtual layers through Python from the author's GitHub:

https://github.com/mhugo/qgis_vlayers/blob/master/README.md