src/providers/ogr/qgsogrprovider.cpp

@@ -556,6 +556,10 @@ void QgsOgrProvider::setRelevantFields( bool fetchGeometry, const QgsAttributeLi
 
     OGR_L_SetIgnoredFields( ogrLayer, ignoredFields.data() );
   }
+
+  // mark that relevant fields may not be set appropriately for nextFeature() calls
+  mRelevantFieldsForNextFeature = false;
+
 #else
   Q_UNUSED( fetchGeometry );
   Q_UNUSED( fetchAttributes );
@@ -623,12 +627,17 @@ bool QgsOgrProvider::nextFeature( QgsFeature& feature )
     return false;
   }
 
+  if ( !mRelevantFieldsForNextFeature )
+  {
+    // setting relevant fields has some overhead so set it only when necessary
+    setRelevantFields( mFetchGeom || mUseIntersect || !mFetchRect.isEmpty(),
+                       mAttributesToFetch );
+    mRelevantFieldsForNextFeature = true;
+  }
+
   OGRFeatureH fet;
   QgsRectangle selectionRect;
 
-  setRelevantFields( mFetchGeom || mUseIntersect || !mFetchRect.isEmpty(),
-                     mAttributesToFetch );
-
   while (( fet = OGR_L_GetNextFeature( ogrLayer ) ) )
   {
     // skip features without geometry
@@ -727,6 +736,10 @@ void QgsOgrProvider::select( QgsAttributeList fetchAttributes, QgsRectangle rect
   mFetchGeom = fetchGeometry;
   mFetchRect = rect;
 
+  setRelevantFields( mFetchGeom || mUseIntersect || !mFetchRect.isEmpty(),
+                     mAttributesToFetch );
+  mRelevantFieldsForNextFeature = true;
+
   // spatial query to select features
   if ( rect.isEmpty() )
   {

src/providers/ogr/qgsogrprovider.h

@@ -334,6 +334,13 @@ class QgsOgrProvider : public QgsVectorDataProvider
     int geomType;
     long featuresCounted;
 
+    /** Flag whether OGR will return fields required by nextFeature() calls.
+        The relevant fields are first set in select(), however the setting may be
+        interferred by some other calls. This flag ensures they are set again
+        to correct values.
+     */
+    bool mRelevantFieldsForNextFeature;
+
     //! Selection rectangle
     OGRGeometryH mSelectionRectangle;
     /**Adds one feature*/