Utilise expression context cache to store some more expensive

expression calculation results

(cherry-picked from 0f1c8df)

Author: nyalldawson

src/core/expression/qgsexpressionfunction.cpp

@@ -3418,7 +3418,7 @@ static QVariant fcnGetFeatureById( const QVariantList &values, const QgsExpressi
   return result;
 }
 
-static QVariant fcnGetFeature( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
+static QVariant fcnGetFeature( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction * )
 {
   //arguments: 1. layer id / name, 2. key attribute, 3. eq value
   QgsVectorLayer *vl = QgsExpressionUtils::getVectorLayer( values.at( 0 ), parent );
@@ -3437,6 +3437,13 @@ static QVariant fcnGetFeature( const QVariantList &values, const QgsExpressionCo
   }
 
   const QVariant &attVal = values.at( 2 );
+
+  const QString cacheValueKey = QStringLiteral( "getfeature:%1:%2:%3" ).arg( vl->id() ).arg( attributeId ).arg( attVal.toString() );
+  if ( context && context->hasCachedValue( cacheValueKey ) )
+  {
+    return context->cachedValue( cacheValueKey );
+  }
+
   QgsFeatureRequest req;
   req.setFilterExpression( QStringLiteral( "%1=%2" ).arg( QgsExpression::quotedColumnRef( attribute ),
                            QgsExpression::quotedString( attVal.toString() ) ) );
@@ -3448,10 +3455,15 @@ static QVariant fcnGetFeature( const QVariantList &values, const QgsExpressionCo
   QgsFeatureIterator fIt = vl->getFeatures( req );
 
   QgsFeature fet;
+  QVariant res;
   if ( fIt.nextFeature( fet ) )
-    return QVariant::fromValue( fet );
+  {
+    res = QVariant::fromValue( fet );
+  }
 
-  return QVariant();
+  if ( context )
+    context->setCachedValue( cacheValueKey, res );
+  return res;
 }
 
 static QVariant fcnRepresentValue( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node )
@@ -3481,7 +3493,14 @@ static QVariant fcnRepresentValue( const QVariantList &values, const QgsExpressi
     }
     else
     {
-      QgsVectorLayer *layer = QgsExpressionUtils::getVectorLayer( context->variable( "layer" ), parent );
+      QgsVectorLayer *layer = QgsExpressionUtils::getVectorLayer( context->variable( QStringLiteral( "layer" ) ), parent );
+
+      const QString cacheValueKey = QStringLiteral( "repvalfcnval:%1:%2:%3" ).arg( layer ? layer->id() : QStringLiteral( "[None]" ), fieldName, value.toString() );
+      if ( context->hasCachedValue( cacheValueKey ) )
+      {
+        return context->cachedValue( cacheValueKey );
+      }
+
       const QgsEditorWidgetSetup setup = fields.at( fieldIndex ).editorWidgetSetup();
       const QgsFieldFormatter *formatter = QgsApplication::fieldFormatterRegistry()->fieldFormatter( setup.type() );
 
@@ -3497,6 +3516,8 @@ static QVariant fcnRepresentValue( const QVariantList &values, const QgsExpressi
         cache = context->cachedValue( cacheKey );
 
       result = formatter->representValue( layer, fieldIndex, setup.config(), cache, value );
+
+      context->setCachedValue( cacheValueKey, result );
     }
   }
   else