Auto populate field as concatenation of other fields

Question

I'm searching for a way to automatically combine several field values entered in the feature edit dialogue, resulting in a new column comprised of the former values.

I have, say fields A, B and C that will be edited manually with the edit form, where i.e. 'A-text', 'B-text' and so on, are inserted. Field D should then automatically be filled with the concatenated string: 'A-text, something, B-text, something, C-text, something'.

Is a custom ui-file necessary for this? I found this promissing post How to automatically populate fields instantly? but was not able to adapt it for my purpose..

Answer 1

..digging the WWW I eventually found a solution, which in fact is quite straight forward.

So, here's my solution for the record: 'Name', 'Region',.. correspond to column A, B,.. from above, and the html-markup that is inserted on the fly corresponds to 'something'

Python-Script (markupForm.py)

from PyQt4.QtCore import *
from PyQt4.QtGui import *

def formOpen(dialog,layerid,featureid): 
    global nameField
    nameField = dialog.findChild(QLineEdit,"Name")
    global regionField
    regionField = dialog.findChild(QLineEdit,"Region")
    global altField
    altField = dialog.findChild(QLineEdit,"Altitude")
    global difficField
    difficField = dialog.findChild(QLineEdit,"Difficulty")
    global riskField
    riskField = dialog.findChild(QLineEdit,"Risk")
    global uphillField
    uphillField = dialog.findChild(QLineEdit,"Uphill")
    global valueField
    valueField = dialog.findChild(QLineEdit,"Value")
    global shuttleField
    shuttleField = dialog.findChild(QLineEdit,"Shuttle")
    global conflField
    conflField = dialog.findChild(QLineEdit,"Conflict") 
    global descrField
    descrField = dialog.findChild(QPlainTextEdit,"Description")
    nameField.textChanged.connect( newDescr )
    regionField.textChanged.connect( newDescr )
    altField.textChanged.connect( newDescr )
    difficField.textChanged.connect( newDescr )
    riskField.textChanged.connect( newDescr )
    uphillField.textChanged.connect( newDescr )
    valueField.textChanged.connect( newDescr )
    shuttleField.textChanged.connect( newDescr )
    conflField.textChanged.connect( newDescr )

def newDescr():
    descrField.setPlainText('<div id="topic" style="float:left; font-weight:bold; padding-right:10px;">Name:</br>Region:</br>H&ouml;ehendifferenz:</br>Schwierigkeit:</br>Gefahr:</br>Erlebnis:</br>Aufstiegshilfe:</br>Uphill:</br>Konflikt:</div><div id="topic-text" style="width:330px;">' +    
    nameField.text() + '</br>' + regionField.text() + '</br>' + altField.text() + '</br>' +
    difficField.text() + '</br>' + riskField.text() + '</br>' + uphillField.text() + '</br>' + valueField.text() + '</br>' +
    shuttleField.text() + '</br>' + conflField.text() + '</div>')

Answer 2

Recommended / Built-in Approach: Use the built-in "Field Calculator" tool.

1. Select the vector layer
2. Enable edit mode by clicking "Toggle editing"
3. Click "Open Field Calculator" (only clickable when in edit mode)
4. Add settings for the new field including fieldname and type: "Text (string)"
5. Use the concat function. e.g. concat(fieldA,fieldB,fieldC) or to join parts with a space character use concat(fieldA,' ',fieldB,' ',fieldC)

(Using QGIS 2.0.1)

Alternative: Using OpenOffice Calc to edit DBF directly.

My preferred (alternative) solution is to actually edit the DBF file manually using OpenOffice Calc. It avoids the need to write python code.

The first row contains the field heading & type. Rather than creating this manually, I recommend adding the empty column first in QGIS with the correct field type. Then re-open the DBF in OpenOffice and make your updates.

Just don't change any column headers or re-order any rows when editing the DBF.