Expression context creation for processing improvements

m-kuhn · m-kuhn · commit abe1a9b66186 · 2017-11-24T16:09:05.000+01:00
Hiding away the implementation directly in QgsProcessingFeatureSource See discussion https://github.com/qgis/QGIS/pull/5709/files/ec97102bc687cdd3aace40359b67c9e45913b726#r152903378
diff --git a/python/core/processing/qgsprocessingutils.sip b/python/core/processing/qgsprocessingutils.sip
@@ -274,10 +274,11 @@ class QgsProcessingFeatureSource : QgsFeatureSource
     virtual QVariant maximumValue( int fieldIndex ) const;
 
 
-    QgsFeatureSource *source() const;
+    QgsExpressionContext createExpressionContext( const QgsProcessingContext &context ) const;
 %Docstring
- Access the underlying original ``source``.
- :rtype: QgsFeatureSource
+ Returns an expression context scope suitable for this source or a default global/project
+ context if nothing more specific can be created.
+ :rtype: QgsExpressionContext
 %End
 
 };
diff --git a/src/core/processing/qgsprocessingalgorithm.cpp b/src/core/processing/qgsprocessingalgorithm.cpp
@@ -132,22 +132,16 @@ QgsExpressionContext QgsProcessingAlgorithm::createExpressionContext( const QVar
   // If there's a source capable of generating a context scope, use it
   if ( source )
   {
-    QgsExpressionContextGenerator *generator = dynamic_cast<QgsExpressionContextGenerator *>( source->source() );
-    if ( generator )
-    {
-      const auto &scopes = generator->createExpressionContext().takeScopes();
-      for ( QgsExpressionContextScope *scope : scopes )
-        c << scope;
-    }
+    const auto &scopes = source->createExpressionContext( context ).takeScopes();
+    for ( QgsExpressionContextScope *scope : scopes )
+      c << scope;
+  }
+  else if ( c.scopeCount() == 0 )
+  {
+    //empty scope, populate with initial scopes
+    c << QgsExpressionContextUtils::globalScope()
+      << QgsExpressionContextUtils::projectScope( context.project() );
   }
-  else
-
-    if ( c.scopeCount() == 0 )
-    {
-      //empty scope, populate with initial scopes
-      c << QgsExpressionContextUtils::globalScope()
-        << QgsExpressionContextUtils::projectScope( context.project() );
-    }
 
   c << QgsExpressionContextUtils::processingAlgorithmScope( this, parameters, context );
   return c;
diff --git a/src/core/processing/qgsprocessingutils.cpp b/src/core/processing/qgsprocessingutils.cpp
@@ -721,7 +721,19 @@ QVariant QgsProcessingFeatureSource::maximumValue( int fieldIndex ) const
   return mSource->maximumValue( fieldIndex );
 }
 
-QgsFeatureSource *QgsProcessingFeatureSource::source() const
+QgsExpressionContext QgsProcessingFeatureSource::createExpressionContext( const QgsProcessingContext &context ) const
 {
-  return mSource;
+  QgsExpressionContext expressionContext;
+  QgsExpressionContextGenerator *generator = dynamic_cast<QgsExpressionContextGenerator *>( mSource );
+  if ( generator )
+  {
+    expressionContext = generator->createExpressionContext();
+  }
+  else
+  {
+    expressionContext
+        << QgsExpressionContextUtils::globalScope()
+        << QgsExpressionContextUtils::projectScope( context.project() );
+  }
+  return expressionContext;
 }
diff --git a/src/core/processing/qgsprocessingutils.h b/src/core/processing/qgsprocessingutils.h
@@ -320,9 +320,10 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
     QVariant maximumValue( int fieldIndex ) const override;
 
     /**
-     * Access the underlying original \a source.
+     * Returns an expression context scope suitable for this source or a default global/project
+     * context if nothing more specific can be created.
      */
-    QgsFeatureSource *source() const;
+    QgsExpressionContext createExpressionContext( const QgsProcessingContext &context ) const;
 
   private:
 
