Merge pull request #4848 from nyalldawson/virtual_agg

Fix aggregate calculation in virtual fields

Author: nyalldawson

python/core/qgsvectorlayerfeatureiterator.sip

@@ -61,6 +61,7 @@ class QgsVectorLayerFeatureSource : QgsAbstractFeatureSource
 
 
 
+
 };
 
 

src/core/qgsvectorlayerfeatureiterator.cpp

@@ -79,6 +79,9 @@ QgsVectorLayerFeatureSource::QgsVectorLayerFeatureSource( const QgsVectorLayer *
     }
 #endif
   }
+
+  std::unique_ptr< QgsExpressionContextScope > layerScope( QgsExpressionContextUtils::layerScope( layer ) );
+  mLayerScope = *layerScope;
 }
 
 QgsVectorLayerFeatureSource::~QgsVectorLayerFeatureSource()
@@ -614,6 +617,15 @@ void QgsVectorLayerFeatureIterator::prepareExpression( int fieldIdx )
   exp->setAreaUnits( QgsProject::instance()->areaUnits() );
 
   exp->prepare( mExpressionContext.get() );
+  Q_FOREACH ( const QString &col, exp->referencedColumns() )
+  {
+    if ( mSource->fields().lookupField( col ) == fieldIdx )
+    {
+      // circular reference - expression depends on column itself
+      delete exp;
+      return;
+    }
+  }
   mExpressionFieldInfo.insert( fieldIdx, exp );
 
   Q_FOREACH ( const QString &col, exp->referencedColumns() )
@@ -644,7 +656,7 @@ void QgsVectorLayerFeatureIterator::prepareFields()
   mExpressionContext.reset( new QgsExpressionContext() );
   mExpressionContext->appendScope( QgsExpressionContextUtils::globalScope() );
   mExpressionContext->appendScope( QgsExpressionContextUtils::projectScope( QgsProject::instance() ) );
-  mExpressionContext->setFields( mSource->mFields );
+  mExpressionContext->appendScope( new QgsExpressionContextScope( mSource->mLayerScope ) );
 
   mFieldsToPrepare = ( mRequest.flags() & QgsFeatureRequest::SubsetOfAttributes ) ? mRequest.subsetOfAttributes() : mSource->mFields.allAttributesList();
 

src/core/qgsvectorlayerfeatureiterator.h

@@ -84,6 +84,8 @@ class CORE_EXPORT QgsVectorLayerFeatureSource : public QgsAbstractFeatureSource
 
     QgsFields mFields;
 
+    QgsExpressionContextScope mLayerScope;
+
     bool mHasEditBuffer;
 
     // A deep-copy is only performed, if the original maps change

tests/src/python/test_qgsvectorlayer.py

@@ -1609,6 +1609,11 @@ def test_ExpressionField(self):
 
         self.assertEqual(layer.pendingFields().count(), cnt)
 
+        # expression field which references itself
+        idx = layer.addExpressionField('sum(test2)', QgsField('test2', QVariant.LongLong))
+        fet = next(layer.getFeatures())
+        self.assertEqual(fet['test2'], NULL)
+
     def test_ExpressionFieldEllipsoidLengthCalculation(self):
         #create a temporary layer
         temp_layer = QgsVectorLayer("LineString?crs=epsg:3111&field=pk:int", "vl", "memory")
@@ -1829,6 +1834,27 @@ def testAggregate(self):
         self.assertTrue(ok)
         self.assertEqual(val, 'this is a test')
 
+    def testAggregateInVirtualField(self):
+        """
+        Test aggregates in a virtual field
+        """
+        layer = QgsVectorLayer("Point?field=fldint:integer", "layer", "memory")
+        pr = layer.dataProvider()
+
+        int_values = [4, 2, 3, 2, 5, None, 8]
+        features = []
+        for i in int_values:
+            f = QgsFeature()
+            f.setFields(layer.fields())
+            f.setAttributes([i])
+            features.append(f)
+        assert pr.addFeatures(features)
+
+        field = QgsField('virtual', QVariant.Double)
+        layer.addExpressionField('sum(fldint*2)', field)
+        vals = [f['virtual'] for f in layer.getFeatures()]
+        self.assertEqual(vals, [48, 48, 48, 48, 48, 48, 48])
+
     def onLayerOpacityChanged(self, tr):
         self.opacityTest = tr