[attribute form] Properly handle default value using current_parent_* variable/function when in editing state

src/gui/qgsattributeform.cpp

@@ -615,6 +615,28 @@ void QgsAttributeForm::updateValuesDependenciesVirtualFields( const int originId
   }
 }
 
+void QgsAttributeForm::updateValuesDependenciesParent()
+{
+  // create updated Feature
+  QgsFeature updatedFeature = getUpdatedFeature();
+  QList<int> updatedFields;
+
+  // go through fields dependent to parent feature value(s)
+  const QSet<QgsEditorWidgetWrapper *> relevantWidgets = mParentDependencies;
+  for ( QgsEditorWidgetWrapper *eww : relevantWidgets )
+  {
+    //do not update when this widget is already updating (avoid recursions)
+    if ( updatedFields.contains( eww->fieldIdx() ) )
+      continue;
+
+    // Update value
+    updatedFields << eww->fieldIdx();
+    QgsExpressionContext context = createExpressionContext( updatedFeature );
+    const QVariant value = mLayer->defaultValue( eww->fieldIdx(), updatedFeature, &context );
+    eww->setValue( value );
+  }
+}
+
 void QgsAttributeForm::updateRelatedLayerFields()
 {
   // Synchronize dependencies
@@ -1527,6 +1549,15 @@ void QgsAttributeForm::refreshFeature()
 
 void QgsAttributeForm::parentFormValueChanged( const QString &attribute, const QVariant &newValue )
 {
+  if ( mContext.parentFormFeature().isValid() )
+  {
+    QgsFeature parentFormFeature = mContext.parentFormFeature();
+    parentFormFeature.setAttribute( attribute, newValue );
+    mContext.setParentFormFeature( parentFormFeature );
+  }
+
+  updateValuesDependenciesParent();
+
   for ( QgsWidgetWrapper *ww : std::as_const( mWidgets ) )
   {
     QgsEditorWidgetWrapper *eww = qobject_cast<QgsEditorWidgetWrapper *>( ww );
@@ -3147,6 +3178,7 @@ void QgsAttributeForm::updateFieldDependencies()
   mDefaultValueDependencies.clear();
   mVirtualFieldsDependencies.clear();
   mRelatedLayerFieldsDependencies.clear();
+  mParentDependencies.clear();
 
   //create defaultValueDependencies
   for ( QgsWidgetWrapper *ww : std::as_const( mWidgets ) )
@@ -3155,6 +3187,7 @@ void QgsAttributeForm::updateFieldDependencies()
     if ( ! eww )
       continue;
 
+    updateFieldDependenciesParent( eww );
     updateFieldDependenciesDefaultValue( eww );
     updateFieldDependenciesVirtualFields( eww );
     updateRelatedLayerFieldsDependencies( eww );
@@ -3245,6 +3278,23 @@ void QgsAttributeForm::updateRelatedLayerFieldsDependencies( QgsEditorWidgetWrap
   }
 }
 
+void QgsAttributeForm::updateFieldDependenciesParent( QgsEditorWidgetWrapper *eww )
+{
+  if ( eww && !eww->field().defaultValueDefinition().expression().isEmpty() )
+  {
+    const QgsExpression expression( eww->field().defaultValueDefinition().expression() );
+    const QSet< QString > referencedVariablesAndFunctions = expression.referencedVariables() + expression.referencedFunctions();
+    for ( const QString &referenced : referencedVariablesAndFunctions )
+    {
+      if ( referenced.startsWith( QStringLiteral( "current_parent" ) ) )
+      {
+        mParentDependencies.insert( eww );
+        break;
+      }
+    }
+  }
+}
+
 void QgsAttributeForm::setMultiEditFeatureIdsRelations( const QgsFeatureIds &fids )
 {
   for ( QgsAttributeFormWidget *formWidget : mFormWidgets )

src/gui/qgsattributeform.h

@@ -387,6 +387,7 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     void updateFieldDependenciesDefaultValue( QgsEditorWidgetWrapper *eww );
     void updateFieldDependenciesVirtualFields( QgsEditorWidgetWrapper *eww );
     void updateRelatedLayerFieldsDependencies( QgsEditorWidgetWrapper *eww = nullptr );
+    void updateFieldDependenciesParent( QgsEditorWidgetWrapper *eww );
 
     void setMultiEditFeatureIdsRelations( const QgsFeatureIds &fids );
 
@@ -422,6 +423,7 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     void updateValuesDependencies( const int originIdx );
     void updateValuesDependenciesDefaultValues( const int originIdx );
     void updateValuesDependenciesVirtualFields( const int originIdx );
+    void updateValuesDependenciesParent();
     void updateRelatedLayerFields();
 
     void clearMultiEditMessages();
@@ -555,6 +557,8 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
      */
     QSet<QgsEditorWidgetWrapper *> mRelatedLayerFieldsDependencies;
 
+    QSet<QgsEditorWidgetWrapper *> mParentDependencies;
+
     //! List of updated fields to avoid recursion on the setting of defaultValues
     QList<int> mAlreadyUpdatedFields;
 

tests/src/gui/testqgsattributeform.cpp

@@ -58,6 +58,7 @@ class TestQgsAttributeForm : public QObject
     void testAttributeFormInterface();
     void testDefaultValueUpdate();
     void testDefaultValueUpdateRecursion();
+    void testParentFeatureUpdate();
     void testSameFieldSync();
     void testZeroDoubles();
     void testMinimumWidth();
@@ -1111,6 +1112,38 @@ void TestQgsAttributeForm::testDefaultValueUpdateRecursion()
   QCOMPARE( ww3->value().toInt(), 43 );
 }
 
+void TestQgsAttributeForm::testParentFeatureUpdate()
+{
+  // make a temporary layer to check through
+  const QString def = QStringLiteral( "Point?field=col0:integer" );
+  QgsVectorLayer *layer = new QgsVectorLayer( def, QStringLiteral( "test" ), QStringLiteral( "memory" ) );
+  layer->setDefaultValueDefinition( 0, QgsDefaultValue( QStringLiteral( "current_parent_value('colZero\')" ), true ) );
+  layer->startEditing();
+
+  // initialize parent feature
+  QgsFields parentFields;
+  parentFields.append( QgsField( QStringLiteral( "colZero" ), QMetaType::Type::Int ) );
+
+  QgsFeature parentFeature( parentFields, 1 );
+  parentFeature.setAttribute( QStringLiteral( "colZero" ), 10 );
+
+  // initialize child feature
+  QgsFeature feature( layer->dataProvider()->fields(), 1 );
+
+  // build a form
+  QgsAttributeEditorContext context;
+  context.setParentFormFeature( parentFeature );
+  QgsAttributeForm form( layer, feature, context );
+
+  // get wrappers for each widget
+  QgsEditorWidgetWrapper *ww0;
+  ww0 = qobject_cast<QgsEditorWidgetWrapper *>( form.mWidgets[0] );
+
+  form.parentFormValueChanged( QStringLiteral( "colZero" ), 20 );
+
+  QCOMPARE( ww0->value().toInt(), 20 );
+}
+
 void TestQgsAttributeForm::testSameFieldSync()
 {
   // Check that widget synchronisation works when a form contains the same field several times