3

As seen here, it is possible to use PyQGIS to load layers from PostgreSQL using an instance of QgsDataSourceUri(). You then set the connection and load a layer.

Loading PostGIS layer from SQL query using PyQGIS

uri = QgsDataSourceUri()
uri.setConnection("localhost", "5432", "myBase", "myUser", "myPassword")

In QGIS our users will have standardized named connections in the QGIS data browser, something along the lines of 'GIS-DATA' to connect to the GIS database etc. Is there a way to leverage using something like the following to avoid having to parse out all of the parameters each time?

uri = QgsDataSourceUri()
uri.setConnection("GIS-DATA")

Using named connections seems to be possible in Processing Algorithms (ex- see the PostgreSQL Execute and Load SQL tool, it has a parameter for 'connection name'). https://docs.qgis.org/3.28/en/docs/user_manual/processing_algs/qgis/database.html#export-to-postgresql

Is there a way to access this connection to add and load layers?

2 Answers 2

7

Ah I think I actually figured it out from this page: Getting schema names from PostGIS database in PyQGIS

For connections that exist, you can use:

md = QgsProviderRegistry.instance().providerMetadata('postgres')
conn2 = md.createConnection('GIS-DATA')

instead of the following to create new ones:

uri = QgsDataSourceUri()
uri.setConnection("localhost", "5432", "GIS-DATA", "postgres", "postgres")

7

Try this. I have a connection called localhost data so I search for the word data in all the PostgreSQL connections:

from PyQt5.QtCore import QSettings
qs = QSettings()
L = []
for k in sorted(qs.allKeys()): #For all stored settings
     if all([word in k.lower() for word in ("postgresql", "data")]): #If the setting have both postgresql and data in it
        print(k)
        L.append(k)
#prints out all setting keys with the word postgresql and data in them, like:
#PostgreSQL/connections/localhost data/database
#PostgreSQL/connections/localhost data/host
#...
#And appends them to L list

#We need to pass each key to qs.value. For example qs.value("PostgreSQL/connections/localhost data/username")
#  to get the username

conn = '/'.join(L[0].split("/")[:-1])+"/" #Create the first part of the key
#'PostgreSQL/connections/localhost data/'

#Fetch the values
keywords = ["host", "port", "database", "username", "password"] #Each keyword and the conn string needs to be combined and passed to qs.value
host, port, database, username, password = [qs.value(f"{conn}{key}") for key in keywords] #Fetch the values we need

#Add a table called land in the public schema using the parameters
uri = QgsDataSourceUri()
uri.setConnection(host, port, database, username, password)
uri.setDataSource("public", "land", "geom")
vlayer = QgsVectorLayer(uri.uri(False), "layer name you like", "postgres")
QgsProject.instance().addMapLayer(vlayer)

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