feature iterator: include attributes required by virtual fields first so that

they trigger joins if necessary (fixes #11545)

Author: jef-n

src/core/qgsvectorlayerfeatureiterator.cpp

@@ -90,13 +90,12 @@ QgsVectorLayerFeatureIterator::QgsVectorLayerFeatureIterator( QgsVectorLayerFeat
     , mFetchedFid( false )
     , mEditGeometrySimplifier( 0 )
 {
+  prepareExpressions();
 
   // prepare joins: may add more attributes to fetch (in order to allow join)
   if ( mSource->mJoinBuffer->containsJoins() )
     prepareJoins();
 
-  prepareExpressions();
-
   mHasVirtualAttributes = !mFetchJoinInfo.isEmpty() || !mExpressionFieldInfo.isEmpty();
 
   // by default provider's request is the same
@@ -507,7 +506,7 @@ void QgsVectorLayerFeatureIterator::prepareExpressions()
         if ( mRequest.flags() & QgsFeatureRequest::SubsetOfAttributes )
         {
           QgsAttributeList attrs;
-          Q_FOREACH ( const QString& col, exp->referencedColumns() )
+          Q_FOREACH( const QString& col, exp->referencedColumns() )
           {
             attrs.append( mSource->mFields.fieldNameIndex( col ) );
           }