From c5f65359d8975dd03f180e8287c701933713f6ae Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Mon, 27 Nov 2017 07:55:05 +1000
Subject: [PATCH] Cache field lookup when evaluating field-based property
 values

---
 src/core/qgsproperty.cpp | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/core/qgsproperty.cpp b/src/core/qgsproperty.cpp
index df1bd5e35c8..936e3147549 100644
--- a/src/core/qgsproperty.cpp
+++ b/src/core/qgsproperty.cpp
@@ -448,14 +448,13 @@ QVariant QgsProperty::propertyValue( const QgsExpressionContext &context, const
           *ok = true;
         return f.attribute( d->cachedFieldIdx );
       }
-
-      int fieldIdx = f.fieldNameIndex( d->fieldName );
-      if ( fieldIdx < 0 )
+      prepare( context );
+      if ( d->cachedFieldIdx < 0 )
         return defaultValue;
 
       if ( ok )
         *ok = true;
-      return f.attribute( fieldIdx );
+      return f.attribute( d->cachedFieldIdx );
     }
 
     case ExpressionBasedProperty: