Allow adding sources to processing expression context

m-kuhn · m-kuhn · commit 851adb0a3d0a · 2017-11-23T15:24:40.000+01:00
diff --git a/python/core/processing/qgsprocessingalgorithm.sip b/python/core/processing/qgsprocessingalgorithm.sip
@@ -326,10 +326,12 @@ class QgsProcessingAlgorithm
 %End
 
     QgsExpressionContext createExpressionContext( const QVariantMap &parameters,
-        QgsProcessingContext &context ) const;
+        QgsProcessingContext &context, QgsProcessingFeatureSource *source = 0 ) const;
 %Docstring
  Creates an expression context relating to the algorithm. This can be called by algorithms
  to create a new expression context ready for evaluating expressions within the algorithm.
+ Optionally, a ``source`` can be specified which will be used to populate the context if it
+ implements the QgsExpressionContextGenerator interface.
  :rtype: QgsExpressionContext
 %End
 
diff --git a/python/core/processing/qgsprocessingutils.sip b/python/core/processing/qgsprocessingutils.sip
@@ -274,6 +274,12 @@ class QgsProcessingFeatureSource : QgsFeatureSource
     virtual QVariant maximumValue( int fieldIndex ) const;
 
 
+    QgsFeatureSource *source() const;
+%Docstring
+ Access the underlying original ``source``.
+ :rtype: QgsFeatureSource
+%End
+
 };
 
 
diff --git a/python/core/qgsexpressioncontext.sip b/python/core/qgsexpressioncontext.sip
@@ -562,6 +562,7 @@ Constructor for QgsExpressionContext
 %End
 
 
+
     void setFeature( const QgsFeature &feature );
 %Docstring
  Convenience function for setting a feature for the context. The feature
diff --git a/src/core/processing/qgsprocessingalgorithm.cpp b/src/core/processing/qgsprocessingalgorithm.cpp
@@ -124,16 +124,30 @@ QWidget *QgsProcessingAlgorithm::createCustomParametersWidget( QWidget * ) const
 }
 
 QgsExpressionContext QgsProcessingAlgorithm::createExpressionContext( const QVariantMap &parameters,
-    QgsProcessingContext &context ) const
+    QgsProcessingContext &context, QgsProcessingFeatureSource *source ) const
 {
   // start with context's expression context
   QgsExpressionContext c = context.expressionContext();
-  if ( c.scopeCount() == 0 )
+
+  // If there's a source capable of generating a context scope, use it
+  if ( source )
   {
-    //empty scope, populate with initial scopes
-    c << QgsExpressionContextUtils::globalScope()
-      << QgsExpressionContextUtils::projectScope( context.project() );
+    QgsExpressionContextGenerator *generator = dynamic_cast<QgsExpressionContextGenerator *>( source->source() );
+    if ( generator )
+    {
+      const auto &scopes = generator->createExpressionContext().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() );
+    }
 
   c << QgsExpressionContextUtils::processingAlgorithmScope( this, parameters, context );
   return c;
diff --git a/src/core/processing/qgsprocessingalgorithm.h b/src/core/processing/qgsprocessingalgorithm.h
@@ -339,9 +339,11 @@ class CORE_EXPORT QgsProcessingAlgorithm
     /**
      * Creates an expression context relating to the algorithm. This can be called by algorithms
      * to create a new expression context ready for evaluating expressions within the algorithm.
+     * Optionally, a \a source can be specified which will be used to populate the context if it
+     * implements the QgsExpressionContextGenerator interface.
      */
     QgsExpressionContext createExpressionContext( const QVariantMap &parameters,
-        QgsProcessingContext &context ) const;
+        QgsProcessingContext &context, QgsProcessingFeatureSource *source = nullptr ) const;
 
     /**
      * Checks whether the coordinate reference systems for the specified set of \a parameters
diff --git a/src/core/processing/qgsprocessingutils.cpp b/src/core/processing/qgsprocessingutils.cpp
@@ -695,3 +695,8 @@ QVariant QgsProcessingFeatureSource::maximumValue( int fieldIndex ) const
 {
   return mSource->maximumValue( fieldIndex );
 }
+
+QgsFeatureSource *QgsProcessingFeatureSource::source() const
+{
+  return mSource;
+}
diff --git a/src/core/processing/qgsprocessingutils.h b/src/core/processing/qgsprocessingutils.h
@@ -317,6 +317,11 @@ class CORE_EXPORT QgsProcessingFeatureSource : public QgsFeatureSource
     QVariant minimumValue( int fieldIndex ) const override;
     QVariant maximumValue( int fieldIndex ) const override;
 
+    /**
+     * Access the underlying original \a source.
+     */
+    QgsFeatureSource *source() const;
+
   private:
 
     QgsFeatureSource *mSource = nullptr;
diff --git a/src/core/qgsexpressioncontext.cpp b/src/core/qgsexpressioncontext.cpp
@@ -474,6 +474,13 @@ QgsExpressionContextScope *QgsExpressionContext::popScope()
   return nullptr;
 }
 
+QList<QgsExpressionContextScope *> QgsExpressionContext::takeScopes()
+{
+  QList<QgsExpressionContextScope *> stack = mStack;
+  mStack.clear();
+  return stack;
+}
+
 QgsExpressionContext &QgsExpressionContext::operator<<( QgsExpressionContextScope *scope )
 {
   mStack.append( scope );
diff --git a/src/core/qgsexpressioncontext.h b/src/core/qgsexpressioncontext.h
@@ -581,6 +581,16 @@ class CORE_EXPORT QgsExpressionContext
      */
     QgsExpressionContextScope *popScope();
 
+    /**
+     * Return all scopes from this context and remove them, leaving this context without
+     * any context.
+     * Ownership is transferred to the caller.
+     *
+     * \since QGIS 3.0
+     * \note Not available in Python
+     */
+    QList<QgsExpressionContextScope *> takeScopes() SIP_SKIP;
+
     /**
      * Appends a scope to the end of the context. This scope will override
      * any matching variables or functions provided by existing scopes within the

Original file line number	Diff line number	Diff line change
`@@ -695,3 +695,8 @@ QVariant QgsProcessingFeatureSource::maximumValue( int fieldIndex ) const`
`695`	`695`	`{`
`696`	`696`	`return mSource->maximumValue( fieldIndex );`
`697`	`697`	`}`
	`698`	`+`
	`699`	`+QgsFeatureSource *QgsProcessingFeatureSource::source() const`
	`700`	`+{`
	`701`	`+ return mSource;`
	`702`	`+}`
Original file line number	Diff line number	Diff line change
`@@ -474,6 +474,13 @@ QgsExpressionContextScope *QgsExpressionContext::popScope()`
`474`	`474`	`return nullptr;`
`475`	`475`	`}`
`476`	`476`
	`477`	`+QList<QgsExpressionContextScope *> QgsExpressionContext::takeScopes()`
	`478`	`+{`
	`479`	`+ QList<QgsExpressionContextScope *> stack = mStack;`
	`480`	`+ mStack.clear();`
	`481`	`+ return stack;`
	`482`	`+}`
	`483`	`+`
`477`	`484`	`QgsExpressionContext &QgsExpressionContext::operator<<( QgsExpressionContextScope *scope )`
`478`	`485`	`{`
`479`	`486`	`mStack.append( scope );`