Expression functions can dynamically report geometry and columns

qgis · Oct 27, 2016 · 0b3646b · 0b3646b
1 parent adb184e
commit 0b3646b
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Showing 9 changed files with 219 additions and 50 deletions.
diff --git a/doc/api_break.dox b/doc/api_break.dox
@@ -765,9 +765,6 @@ version instead.
 removed. Use QgsExpressionContext variables instead.
 - The replaceExpressionText version which accepts a QgsFeature argument has been removed. Use the QgsExpressionContext
 version instead.
-- QgsExpression::Function::func has been modified to use a QgsExpressionContext argument rather than a QgsFeature.
-- QgsExpression::Function::usesgeometry() has been renamed to usesGeometry()
-- QgsExpression::Function::helptext() has been renamed to helpText()
 - The QgsExpression::Node::eval and prepare versions which take a QgsFeature has been removed, use the QgsExpressionContext versions instead.
 - QgsExpression::Interval has been removed. Use QgsInterval instead.
 - replaceExpressionText() no longer accepts a substitution map parameter. Use expression context variables instead.
@@ -776,7 +773,14 @@ version instead.
 - acceptVisitor() has been removed
 - QgsExpression::referencedColumns() returns QSet<QString> instead of QStringList
 - QgsExpression::Node::referencedColumns() returns QSet<QString> instead of QStringList
-- QgsExpression::Function::referencedColumns() returns QSet<QString> instead of QStringList
+
+QgsExpression::Function       {#qgis_api_break_3_0_QgsExpression_Function}
+-----------------------
+
+- `QgsExpression::Function::func` has been modified to use a `QgsExpressionContext` argument rather than a `QgsFeature`.
+- `QgsExpression::Function::usesgeometry()` has been renamed to `QgsExpression::Function::usesGeometry( const NodeFunction* node )`
+- `QStringList QgsExpression::Function::referencedColumns()` has been changed to `QSet<QString> QgsExpression::Function::referencedColumns( const NodeFunction* node )`
+- `QgsExpression::Function::helptext()` has been renamed to `helpText()`
 
 
 QgsFeature        {#qgis_api_break_3_0_QgsFeature}

diff --git a/python/core/__init__.py b/python/core/__init__.py
@@ -69,10 +69,12 @@ def myfunc(values, *args):
     """
     class QgsExpressionFunction(QgsExpression.Function):
 
-        def __init__(self, func, name, args, group, helptext='', usesgeometry=True, referencedColumns=QgsFeatureRequest.AllAttributes, expandargs=False):
-            QgsExpression.Function.__init__(self, name, args, group, helptext, usesgeometry, referencedColumns)
+        def __init__(self, func, name, args, group, helptext='', usesGeometry=True, referencedColumns=QgsFeatureRequest.AllAttributes, expandargs=False):
+            QgsExpression.Function.__init__(self, name, args, group, helptext)
             self.function = func
             self.expandargs = expandargs
+            self.uses_geometry = usesGeometry
+            self.referenced_columns = referencedColumns
 
         def func(self, values, context, parent):
             feature = None
@@ -89,6 +91,12 @@ def func(self, values, context, parent):
                 parent.setEvalErrorString(str(ex))
                 return None
 
+        def usesGeometry(self, node):
+            return self.uses_geometry
+
+        def referencedColumns(self, node):
+            return self.referenced_columns
+
     helptemplate = string.Template("""<h3>$name function</h3><br>$doc""")
     name = kwargs.get('name', function.__name__)
     helptext = function.__doc__ or ''

diff --git a/python/core/qgsexpression.sip b/python/core/qgsexpression.sip
@@ -306,8 +306,6 @@ class QgsExpression
                   int params,
                   const QString& group,
                   const QString& helpText = QString(),
-                  bool usesGeometry = false,
-                  const QSet<QString>& referencedColumns = QSet<QString>(),
                   bool lazyEval = false,
                   bool handlesNull = false,
                   bool isContextual = false );
@@ -319,8 +317,6 @@ class QgsExpression
                   int params,
                   const QStringList& groups,
                   const QString& helpText = QString(),
-                  bool usesGeometry = false,
-                  const QSet<QString>& referencedColumns = QSet<QString>(),
                   bool lazyEval = false,
                   bool handlesNull = false,
                   bool isContextual = false );
@@ -332,8 +328,6 @@ class QgsExpression
                   const QgsExpression::ParameterList& params,
                   const QString& group,
                   const QString& helpText = QString(),
-                  bool usesGeometry = false,
-                  const QSet<QString>& referencedColumns = QSet<QString>(),
                   bool lazyEval = false,
                   bool handlesNull = false,
                   bool isContextual = false );
@@ -345,8 +339,6 @@ class QgsExpression
                   const QgsExpression::ParameterList& params,
                   const QStringList& groups,
                   const QString& helpText = QString(),
-                  bool usesGeometry = false,
-                  const QSet<QString>& referencedColumns = QSet<QString>(),
                   bool lazyEval = false,
                   bool handlesNull = false,
                   bool isContextual = false );
@@ -366,8 +358,8 @@ class QgsExpression
         */
         const QgsExpression::ParameterList& parameters() const;
 
-        /** Does this function use a geometry object. */
-        bool usesGeometry() const;
+        //! Does this function use a geometry object.
+        virtual bool usesGeometry( const QgsExpression::NodeFunction* node ) const;
 
         /** Returns a list of possible aliases for the function. These include
          * other permissible names for the function, eg deprecated names.
@@ -382,7 +374,15 @@ class QgsExpression
          */
         bool lazyEval() const;
 
-        virtual QSet<QString> referencedColumns() const;
+        /**
+         * Returns a set of field names which are required for this function.
+         * May contain QgsFeatureRequest::AllAttributes to signal that all
+         * attributes are required.
+         * If in doubt this will return more fields than strictly required.
+         *
+         * @note Added in QGIS 3.0
+         */
+        virtual QSet<QString> referencedColumns( const QgsExpression::NodeFunction* node ) const;
 
         /** Returns whether the function is only available if provided by a QgsExpressionContext object.
          * @note added in QGIS 2.12
@@ -622,7 +622,17 @@ class QgsExpression
         //! @note added in QGIS 2.16
         bool hasNamedNodes() const;
 
-        const QList<QgsExpression::Node*>& list();
+        /**
+         * Get a list of all the nodes.
+         */
+        QList<QgsExpression::Node*> list();
+
+        /**
+         * Get the node at position i in the list.
+         *
+         * @note Added in QGIS 3.0
+         */
+        QgsExpression::Node* at( int i );
 
         //! Returns a list of names for nodes. Unnamed nodes will be indicated by an empty string in the list.
         //! @note added in QGIS 2.16

diff --git a/src/core/qgsexpression.cpp b/src/core/qgsexpression.cpp
@@ -3600,8 +3600,56 @@ const QList<QgsExpression::Function*>& QgsExpression::Functions()
     << new StaticFunction( QStringLiteral( "to_interval" ), ParameterList() << Parameter( QStringLiteral( "value" ) ), fcnToInterval, QStringList() << QStringLiteral( "Conversions" ) << QStringLiteral( "Date and Time" ), QString(), false, QSet<QString>(), false, QStringList() << QStringLiteral( "tointerval" ) )
     << new StaticFunction( QStringLiteral( "coalesce" ), -1, fcnCoalesce, QStringLiteral( "Conditionals" ), QString(), false, QSet<QString>(), false, QStringList(), true )
     << new StaticFunction( QStringLiteral( "if" ), 3, fcnIf, QStringLiteral( "Conditionals" ), QString(), False, QSet<QString>(), true )
-    << new StaticFunction( QStringLiteral( "aggregate" ), ParameterList() << Parameter( QStringLiteral( "layer" ) ) << Parameter( QStringLiteral( "aggregate" ) ) << Parameter( QStringLiteral( "expression" ) )
-                           << Parameter( QStringLiteral( "filter" ), true ) << Parameter( QStringLiteral( "concatenator" ), true ), fcnAggregate, QStringLiteral( "Aggregates" ), QString(), true, QSet<QString>() << QgsFeatureRequest::AllAttributes, true )
+
+    << new StaticFunction( QStringLiteral( "aggregate" ),
+                           ParameterList()
+                           << Parameter( QStringLiteral( "layer" ) )
+                           << Parameter( QStringLiteral( "aggregate" ) )
+                           << Parameter( QStringLiteral( "expression" ) )
+                           << Parameter( QStringLiteral( "filter" ), true )
+                           << Parameter( QStringLiteral( "concatenator" ), true ),
+                           fcnAggregate,
+                           QStringLiteral( "Aggregates" ),
+                           QString(),
+                           []( const QgsExpression::NodeFunction* node )
+    {
+      // usesGeometry callback: return true if @parent variable is referenced
+
+      if ( !node )
+        return true;
+
+      if ( !node->args() || node->args()->count() < 4 )
+        return false;
+      else
+      {
+        QgsExpression::Node* filterNode = node->args()->at( 3 );
+        QSet<QString> referencedVars = filterNode->referencedVariables();
+        return referencedVars.contains( "parent" ) || referencedVars.contains( QString() );
+      }
+    },
+    []( const QgsExpression::NodeFunction* node )
+    {
+      // referencedColumns callback: return AllAttributes if @parent variable is referenced
+
+      if ( !node )
+        return QSet<QString>() << QgsFeatureRequest::AllAttributes;
+
+      if ( !node->args() || node->args()->count() < 4 )
+        return QSet<QString>();
+      else
+      {
+        QgsExpression::Node* filterNode = node->args()->at( 3 );
+        QSet<QString> referencedVars = filterNode->referencedVariables();
+
+        if ( referencedVars.contains( "parent" ) || referencedVars.contains( QString() ) )
+          return QSet<QString>() << QgsFeatureRequest::AllAttributes;
+        else
+          return QSet<QString>();
+      }
+    },
+    true
+                         )
+
     << new StaticFunction( QStringLiteral( "relation_aggregate" ), ParameterList() << Parameter( QStringLiteral( "relation" ) ) << Parameter( QStringLiteral( "aggregate" ) ) << Parameter( QStringLiteral( "expression" ) ) << Parameter( QStringLiteral( "concatenator" ), true ),
                            fcnAggregateRelation, QStringLiteral( "Aggregates" ), QString(), False, QSet<QString>() << QgsFeatureRequest::AllAttributes, true )
 
@@ -4330,14 +4378,14 @@ QSet<QString> QgsExpression::NodeUnaryOperator::referencedVariables() const
   return mOperand->referencedVariables();
 }
 
-QgsExpression::Node*QgsExpression::NodeUnaryOperator::clone() const
+QgsExpression::Node* QgsExpression::NodeUnaryOperator::clone() const
 {
   return new NodeUnaryOperator( mOp, mOperand->clone() );
 }
 
 //
 
-QVariant QgsExpression::NodeBinaryOperator::eval( QgsExpression *parent, const QgsExpressionContext *context )
+QVariant QgsExpression::NodeBinaryOperator::eval( QgsExpression* parent, const QgsExpressionContext* context )
 {
   QVariant vL = mOpLeft->eval( parent, context );
   ENSURE_NO_EVAL_ERROR;
@@ -5009,7 +5057,7 @@ QString QgsExpression::NodeFunction::dump() const
 QSet<QString> QgsExpression::NodeFunction::referencedColumns() const
 {
   Function* fd = Functions()[mFnIndex];
-  QSet<QString> functionColumns = fd->referencedColumns();
+  QSet<QString> functionColumns = fd->referencedColumns( this );
 
   if ( !mArgs )
   {
@@ -5044,7 +5092,7 @@ QSet<QString> QgsExpression::NodeFunction::referencedVariables() const
 
 bool QgsExpression::NodeFunction::needsGeometry() const
 {
-  bool needs = Functions()[mFnIndex]->usesGeometry();
+  bool needs = Functions()[mFnIndex]->usesGeometry( this );
   if ( mArgs )
   {
     Q_FOREACH ( Node* n, mArgs->list() )
@@ -5710,10 +5758,47 @@ QSet<QString> QgsExpression::NodeInOperator::referencedVariables() const
   return lst;
 }
 
+bool QgsExpression::Function::usesGeometry( const QgsExpression::NodeFunction* node ) const
+{
+  Q_UNUSED( node )
+  return true;
+}
+
+QSet<QString> QgsExpression::Function::referencedColumns( const NodeFunction* node ) const
+{
+  Q_UNUSED( node )
+  return QSet<QString>() << QgsFeatureRequest::AllAttributes;
+}
+
 bool QgsExpression::Function::operator==( const QgsExpression::Function& other ) const
 {
   if ( QString::compare( mName, other.mName, Qt::CaseInsensitive ) == 0 )
     return true;
 
   return false;
 }
+
+QgsExpression::StaticFunction::StaticFunction( const QString& fnname, const QgsExpression::ParameterList& params, QgsExpression::FcnEval fcn, const QString& group, const QString& helpText, std::function < bool ( const NodeFunction* node ) > usesGeometry, std::function < QSet<QString>( const NodeFunction* node ) > referencedColumns, bool lazyEval, const QStringList& aliases, bool handlesNull )
+    : Function( fnname, params, group, helpText, lazyEval, handlesNull )
+    , mFnc( fcn )
+    , mAliases( aliases )
+    , mUsesGeometryFunc( usesGeometry )
+    , mReferencedColumnsFunc( referencedColumns )
+{
+}
+
+bool QgsExpression::StaticFunction::usesGeometry( const NodeFunction* node ) const
+{
+  if ( mUsesGeometryFunc )
+    return mUsesGeometryFunc( node );
+  else
+    return mUsesGeometry;
+}
+
+QSet<QString> QgsExpression::StaticFunction::referencedColumns( const NodeFunction* node ) const
+{
+  if ( mReferencedColumnsFunc )
+    return mReferencedColumnsFunc( node );
+  else
+    return mReferencedColumns;
+}