QGIS, creating layer from PostGIS : add a style

Question

I am creating some layers in QGIS using PostgreSQL connection.

I have a python plugin doing the load of the layer in Qgis, this part of the code looks like this :

        uri = QgsDataSourceURI()
        db = SettingsProperties.get_db()
        pg = SettingsProperties.get_postgre_settings()
        uri.setConnection(db['host'], str(db['port']), project_name, pg['user'], pg['password'])
        uri.setDataSource('work', table_name, str(column_geom))

        layer = QgsVectorLayer(uri.uri(), tr(layer_name), "postgres")

No problem with this, but now, I would like to setup style when creating this layer, this relying on the value of some column ... etc

Actually, I am able to setup style through a .qml prepared, but I wanted to know if there is a possibility to create the style either in PostgreSQL or in the Python script in a "simple" way and then add it to the database ?

I know you can save the style with QGIS GUI. But I would like to script it.

Answer 1

There are two possible solutions, that I know: First, is to use a predefined style, saved e.g. in a .qml file. You can than load that .qml file with LAYER_OBJECT.loadNamedStyle(PATH_TO_QML), where PATH_TO_QML obviously point to the file location of the saved style:

layer = QgsVectorLayer(uri.uri(), tr(layer_name), "postgres")
layer.loadNamedStyle(PATH_TO_QML)

Second, you script your own symbology by using a certain renderer object. You'll find examples in the official and famous PyQGIS-Cookbook

You can begin with single-symbol, categorized-symbol or graduated-symbol layer or fine tune with further symbols or your own renderer.