5

I have dozens of layers in QGIS and all these layers have attribute field that I would like to update. I don't want to create new temporal layers with updated fields, rather just update the current layer attribute tables. And I wouldn't want to separately update each layer. I tried field calculator but it creates a new temporal layer. Is there any other solutions that could work? I'm using QGIS 3.22.

enter image description here

8
  • Using field calculator, you have an option to update existing fields. Field calculator does not create new layers, why do you think it does? Describe your workflow and add a screenshot to understand what's going on...
    – Babel
    Commented Dec 21, 2021 at 7:51
  • Field name is 'Modified' and I would need to update the field with a date when the layer have been updated. I'm not familiar with pyqgis but I'm afraid that I won't be able to use that as I would first need to be able to select the layers that have been modified in 1st of December and then update these layers with that date and then I would need to select layers that have been modified in 3rd of December and so on. The modification date is in the layer name.
    – Q-question
    Commented Dec 21, 2021 at 7:56
  • I tried with field calculator and it created this 'calculated' temporal layer. How can I set the field calculator so that it does not create a temporal layer? Then I could run as a batch process and it probably could work for this.
    – Q-question
    Commented Dec 21, 2021 at 8:19
  • Sorry, can you show a screenshot where filed calculator creates a new temporary layer? My field calculator does not! To update an existing field, check the box next to that, see: i.sstatic.net/aaffO.png
    – Babel
    Commented Dec 21, 2021 at 8:43
  • 1
    I added screenshot to my first message. Which version do you use? I noticed that in QGIS 3.4.3 there is option for updating an existing field, but unfortunately there is no option for running as a batch process, so probably is not solution for me in this case.
    – Q-question
    Commented Dec 21, 2021 at 8:47

1 Answer 1

6

You can use pyqgis with re (to find the date) and datetime (to format the date) modules.

The layers must have a 8 digit date somewhere in the layername, formatted like 20211221 (YYYYMMDD). Try it on a subset of layers and backup your data first.

import re, datetime
fieldname = 'modified' #A string field that must exist in each table, change to match your fieldname

patt = r'\d{8}' #Search layername for 8 consecutive digits
for layer in QgsProject.instance().mapLayers().values(): #For each layer added to QGIS
    attrMap = {} #A dictionary to hold feature id: fieldindex:new value
    found = re.search(patt, layer.name()) #Find the 8 digits in a row
    fieldindex = layer.fields().indexFromName(fieldname) #Find the index of "modified" field
    if found:
        oldval = datetime.datetime.strptime(found.group(), '%Y%m%d') #datetime.datetime(2021, 11, 12, 0, 0) #Create a datetime object
        newval = datetime.datetime.strftime(oldval, '%m%d%Y') #Convert to a string in the format you want
        for f in layer.getFeatures():
            attrMap[f.id()] = {fieldindex:newval}
        layer.dataProvider().changeAttributeValues(attrMap)

enter image description here

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.