[Qgis-user] Saving values by a Python-Script in a PostgreSQL-Database

[Kai Behncke]

Dear users,

I try to save attributes in PostgreSQL/PostGIS
by a Python Script.

So far I get a connection and I can set an additional attribute field
that I can fill with a value (it seems so).
But how can I save these values?


My script looks like:

from qgis.core import
QgsApplication,QgsVectorLayer,QgsVectorDataProvider,QgsDataSourceUri
from PyQt5.QtCore import *
from qgis.PyQt.QtSql import QSqlDatabase, QSqlQuery

uri2 = QgsDataSourceUri()
uri2.setConnection("server", "5432", "table", "user", "pw")
#set database schema, table name, geometry column
and optionaly subset(WHERE clause)
uri2.setDataSource ("public", "table", "geom")
# Defining the layer name and layer type for QGIS?
vlayer2=QgsVectorLayer (uri2.uri() ,"ww_manhole","postgres")
print (vlayer2.isValid())
if (vlayer2.startEditing()):
print ("ok startEditing")
else:
print("not ok")
 
my_field_name2 = 'new_field'
if (vlayer2.addAttribute(QgsField(my_field_name2, QVariant.String))):
print ("ok AddAttribute")
else:
print ("not ok2")

my_field_value2 = 'Hello world!'
for f in vlayer2.getFeatures():
print ("ok getFeature")
f[my_field_name2] = my_field_value2
if (vlayer2.updateFeature(f)):
print ("ok updatefeature")
else:
print ("not ok updatefeature")

if (vlayer2.updateFields()):
print ("ok updateFields") 
   else:
print ("not ok updateFields")
if (vlayer2.commitChanges()):
print ("ok commitChanges")
else:
print("not ok commitChanges")



The output shows that neither
updateFields works not commitChanges??
Could anybode help please?

Thank you very much, Kai

The output:

True
ok startEditing
ok AddAttribute
ok getFeature
ok updatefeature
not ok updateFields
not ok commitChanges

Mit freundlichen Grüßen
Im Auftrag

Kai Behncke
Geoinformation
Tel.: +49 5451 931-7125

E-Mail: kai.behn...@ibbenbueren.de 

Rathaus II
Roncallistraße 3-5
1. Stock, Raum 105
49477 Ibbenbüren



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Re: [Qgis-user] Saving values by a Python-Script in a PostgreSQL-Database

[Kai Borgolte]

Hi Kai,

you can get messages from PostGIS by calling commitErrors():

if vlayer2.commitChanges():
print('ok commitChanges')
else:
print('not ok commitChanges')
for l in vlayer2.commitErrors():
print(l)

The messages gave me a subtle hint that the attribute definition has to
be more complete:

if vlayer2.addAttribute(QgsField(my_field_name2, QVariant.String,
'text', -1, -1)):
print('ok AddAttribute')

After this change commitChanges() succeeds. updateFields() continues to
fail without message. I think you don't need updateFields() because you
don't modify fields directly on the provider.
--
Kai Borgolte, Bonn
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