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Use expression filter request for SelectByAttribute

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Makes SelectByAttribute orders of magnitude faster for providers which
support compiled expressions (eg Postgres), also allows algorithm
to take advantage of database indexes created on attribute.

For a 4 million point PostGIS layer (with an index on attribute)
BEFORE: cancelled after 20 mins
AFTER: ~2 seconds
This commit is contained in:
Nyall Dawson 2015-11-13 10:36:21 +11:00
parent fd9f0b5268
commit 7c8177e01a
1 changed files with 7 additions and 13 deletions
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20
python/plugins/processing/algs/qgis/SelectByAttribute.py
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@ -26,7 +26,7 @@ __copyright__ = '(C) 2010, Michael Minn'
__revision__ = '$Format:%H$'
from PyQt4.QtCore import QVariant
from qgis.core import QgsExpression
from qgis.core import QgsExpression, QgsFeatureRequest
from processing.core.GeoAlgorithm import GeoAlgorithm
from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
from processing.core.parameters import ParameterVector
@ -115,18 +115,12 @@ class SelectByAttribute(GeoAlgorithm):
raise GeoAlgorithmExecutionException(
self.tr('Unsupported field type "%s"' % fields[idx].typeName()))
expression = QgsExpression(expr)
expression.prepare(fields)
features = vector.features(layer)
selected = []
count = len(features)
total = 100.0 / float(count)
for count, f in enumerate(features):
if expression.evaluate(f, fields):
selected.append(f.id())
progress.setPercentage(int(count * total))
qExp = QgsExpression(expr)
if not qExp.hasParserError():
qReq = QgsFeatureRequest(qExp)
else:
raise GeoAlgorithmExecutionException(qExp.parserErrorString())
selected = [f.id() for f in layer.getFeatures(qReq)]
layer.setSelectedFeatures(selected)
self.setOutputValue(self.OUTPUT, fileName)