host='localhost'
port="5432"
db='rob'
user='rob'
password='password'

filter = "name = 'M5'"
uri = QgsDataSourceURI()
uri.setConnection(host, port, db, user, password)
uri.setDataSource("public", "dft_major_roads", "geom", filter ,"gid")
print uri.uri()
vlayer = QgsVectorLayer(uri.uri(), "M5", "postgres")
QgsMapLayerRegistry.instance().addMapLayer(vlayer)