Fix joined attributes can't be used in filter expressions

(fix #13176)

src/core/qgsvectorlayerfeatureiterator.cpp

@@ -93,6 +93,23 @@ QgsVectorLayerFeatureIterator::QgsVectorLayerFeatureIterator( QgsVectorLayerFeat
     , mFetchedFid( false )
     , mInterruptionChecker( nullptr )
 {
+  if ( mRequest.filterType() == QgsFeatureRequest::FilterExpression )
+  {
+    mRequest.expressionContext()->setFields( mSource->mFields );
+    mRequest.filterExpression()->prepare( mRequest.expressionContext() );
+
+    if ( mRequest.flags() & QgsFeatureRequest::SubsetOfAttributes )
+    {
+      //ensure that all fields required for filter expressions are prepared
+      Q_FOREACH ( const QString& field, mRequest.filterExpression()->referencedColumns() )
+      {
+        int attrIdx = mSource->mFields.fieldNameIndex( field );
+        if ( !mRequest.subsetOfAttributes().contains( attrIdx ) )
+          mRequest.setSubsetOfAttributes( mRequest.subsetOfAttributes() << attrIdx );
+      }
+    }
+  }
+
   prepareFields();
 
   mHasVirtualAttributes = !mFetchJoinInfo.isEmpty() || !mExpressionFieldInfo.isEmpty();
@@ -173,12 +190,6 @@ QgsVectorLayerFeatureIterator::QgsVectorLayerFeatureIterator( QgsVectorLayerFeat
 
     rewindEditBuffer();
   }
-
-  if ( mRequest.filterType() == QgsFeatureRequest::FilterExpression )
-  {
-    mRequest.expressionContext()->setFields( mSource->mFields );
-    mRequest.filterExpression()->prepare( mRequest.expressionContext() );
-  }
 }
 
 

tests/src/python/test_qgsfeatureiterator.py

@@ -239,7 +239,44 @@ def test_JoinUsingExpression2(self):
         self.assertFalse(fi.nextFeature(f))
 
         QgsMapLayerRegistry.instance().removeMapLayers([layer.id(), joinLayer.id()])
-        # try the other way too
+
+    def test_JoinUsingFeatureRequestExpression(self):
+        """ test requesting features using a filter expression which requires joined columns """
+        joinLayer = QgsVectorLayer(
+            "Point?field=x:string&field=y:integer&field=z:integer",
+            "joinlayer", "memory")
+        pr = joinLayer.dataProvider()
+        f1 = QgsFeature()
+        f1.setAttributes(["foo", 123, 321])
+        f2 = QgsFeature()
+        f2.setAttributes(["bar", 124, 654])
+        self.assertTrue(pr.addFeatures([f1, f2]))
+
+        layer = QgsVectorLayer("Point?field=fldtxt:string&field=fldint:integer",
+                               "addfeat", "memory")
+        pr = layer.dataProvider()
+        f1 = QgsFeature()
+        f1.setAttributes(["test", 123])
+        f2 = QgsFeature()
+        f2.setAttributes(["test", 124])
+        self.assertTrue(pr.addFeatures([f1, f2]))
+
+        QgsMapLayerRegistry.instance().addMapLayers([layer, joinLayer])
+
+        join = QgsVectorJoinInfo()
+        join.targetFieldName = "fldint"
+        join.joinLayerId = joinLayer.id()
+        join.joinFieldName = "y"
+        join.memoryCache = True
+        layer.addJoin(join)
+
+        f = QgsFeature()
+        fi = layer.getFeatures(QgsFeatureRequest().setFlags(QgsFeatureRequest.SubsetOfAttributes).setFilterExpression('joinlayer_z=654'))
+        self.assertTrue(fi.nextFeature(f))
+        self.assertEqual(f['fldint'], 124)
+        self.assertEqual(f['joinlayer_z'], 654)
+
+        QgsMapLayerRegistry.instance().removeMapLayers([layer.id(), joinLayer.id()])
 
 
 if __name__ == '__main__':