I am updating some plugins which use QgsExpression, and I'm wondering about the
best way to use expressions in QGIS3. It in the past I used a pattern like:
exp=QgsExpression(expressionText)
exp.prepare(fields)
request=QgsFeatureRequest()
request.setSubsetOfAttributes( expression.referencedColumns(), fields )
for feat in layer.getFeatures(request)
value=expression.evaluate(feat)
However with QGIS3 this has clearly changed! QgsExpression is not included in
the QGIS3 API https://qgis.org/api/annotated.html. The prepare and
referencedColumns are no longer defined. I did have a look at the C++ code for
QgsExpression, but I find I'm still looking for guidance.
I've searched the QEP issues been able to locate a QEP, or other
documentation. Can anyone point me to some documentation or provide an example
of current best practice please.
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