cache sublayer feature counts and don't retrieve expensive ones (fixes #5322)

Author: jef-n

src/providers/ogr/qgsogrprovider.cpp

@@ -456,18 +456,22 @@ QString QgsOgrProvider::subsetString()
 
 QStringList QgsOgrProvider::subLayers() const
 {
-  QStringList theList = QStringList();
   if ( !valid )
   {
-    return theList;
+    return QStringList();
   }
 
+  if ( !mSubLayerList.isEmpty() )
+    return mSubLayerList;
+
   for ( unsigned int i = 0; i < layerCount() ; i++ )
   {
-    QString theLayerName = FROM8( OGR_FD_GetName( OGR_L_GetLayerDefn( OGR_DS_GetLayer( ogrDataSource, i ) ) ) );
-    OGRwkbGeometryType layerGeomType = OGR_FD_GetGeomType( OGR_L_GetLayerDefn( OGR_DS_GetLayer( ogrDataSource, i ) ) );
+    OGRLayerH layer = OGR_DS_GetLayer( ogrDataSource, i );
+    OGRFeatureDefnH fdef = OGR_L_GetLayerDefn( layer );
+    QString theLayerName = FROM8( OGR_FD_GetName( fdef ) );
+    OGRwkbGeometryType layerGeomType = OGR_FD_GetGeomType( fdef );
 
-    int theLayerFeatureCount = OGR_L_GetFeatureCount( OGR_DS_GetLayer( ogrDataSource, i ), 1 ) ;
+    int theLayerFeatureCount = OGR_L_GetFeatureCount( layer, 0 );
 
     QString geom;
     switch ( layerGeomType )
@@ -486,11 +490,13 @@ QStringList QgsOgrProvider::subLayers() const
       case wkbMultiPoint25D:      geom = "MultiPoint25D"; break;
       case wkbMultiLineString25D: geom = "MultiLineString25D"; break;
       case wkbMultiPolygon25D:    geom = "MultiPolygon25D"; break;
-      default: geom="Unknown WKB: " + QString::number( layerGeomType );
+      default:                    geom = QString( "Unknown WKB: %1" ).arg( layerGeomType );
     }
-    theList.append( QString::number( i ) + ":" + theLayerName + ":" + QString::number( theLayerFeatureCount ) + ":" + geom );
+
+    mSubLayerList << QString( "%1:%2:%3:%4" ).arg( i ).arg( theLayerName ).arg( theLayerFeatureCount ).arg( geom );
   }
-  return theList;
+
+  return mSubLayerList;
 }
 
 void QgsOgrProvider::setEncoding( const QString& e )

src/providers/ogr/qgsogrprovider.h

@@ -338,6 +338,8 @@ class QgsOgrProvider : public QgsVectorDataProvider
     int geomType;
     long featuresCounted;
 
+    mutable QStringList mSubLayerList;
+
     /** 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