Make additional sort caches accessible

Author: m-kuhn

python/gui/auto_generated/attributetable/qgsattributetablemodel.sip.in

@@ -194,14 +194,18 @@ Specify -1 as column to invalidate the cache
     void prefetchSortData( const QString &expression, unsigned long cacheIndex = 0 );
 %Docstring
 Prefetches the entire data for one expression. Based on this cached information
-the sorting can later be done in a performant way.
+the sorting can later be done in a performant way. A ``cacheIndex`` can be specified
+if multiple caches should be filled. In this case, the caches will be available
+as ``QgsAttributeTableModel.SortRole + cacheIndex``.
 
 :param expression: The expression to cache
 %End
 
-    QString sortCacheExpression() const;
+    QString sortCacheExpression( unsigned long cacheIndex = 0 ) const;
 %Docstring
-The expression which was used to fill the sorting cache
+The expression which was used to fill the sorting cache at index \cacheIndex.
+
+.. seealso:: :py:func:`prefetchSortData`
 %End
 
     void setRequest( const QgsFeatureRequest &request );

src/gui/attributetable/qgsattributetablemodel.cpp

@@ -908,13 +908,14 @@ void QgsAttributeTableModel::prefetchSortData( const QString &expressionString,
   }
 }
 
-QString QgsAttributeTableModel::sortCacheExpression() const
+QString QgsAttributeTableModel::sortCacheExpression( unsigned long cacheIndex ) const
 {
-  Q_ASSERT( !mSortCaches.empty() );
-
   QString expressionString;
 
-  const QgsExpression &expression = mSortCaches.begin()->sortCacheExpression;
+  if ( cacheIndex >= mSortCaches.size() )
+    return expressionString;
+
+  const QgsExpression &expression = mSortCaches[cacheIndex].sortCacheExpression;
 
   if ( expression.isValid() )
     expressionString = expression.expression();

src/gui/attributetable/qgsattributetablemodel.h

@@ -200,16 +200,20 @@ class GUI_EXPORT QgsAttributeTableModel: public QAbstractTableModel
 
     /**
      * Prefetches the entire data for one expression. Based on this cached information
-     * the sorting can later be done in a performant way.
+     * the sorting can later be done in a performant way. A \a cacheIndex can be specified
+     * if multiple caches should be filled. In this case, the caches will be available
+     * as ``QgsAttributeTableModel::SortRole + cacheIndex``.
      *
      * \param expression The expression to cache
      */
     void prefetchSortData( const QString &expression, unsigned long cacheIndex = 0 );
 
     /**
-     * The expression which was used to fill the sorting cache
+     * The expression which was used to fill the sorting cache at index \cacheIndex.
+     *
+     *  \see prefetchSortData
      */
-    QString sortCacheExpression() const;
+    QString sortCacheExpression( unsigned long cacheIndex = 0 ) const;
 
     /**
      * Set a request that will be used to fill this attribute table model.