fixes #20893 : Update virtual layer when referenced layer update its fields

Author: troopa81

src/providers/virtual/qgsvirtuallayerprovider.cpp

@@ -132,6 +132,7 @@ bool QgsVirtualLayerProvider::loadSourceLayers()
       connect( vl, &QgsVectorLayer::featureAdded, this, &QgsVirtualLayerProvider::invalidateStatistics );
       connect( vl, &QgsVectorLayer::featureDeleted, this, &QgsVirtualLayerProvider::invalidateStatistics );
       connect( vl, &QgsVectorLayer::geometryChanged, this, &QgsVirtualLayerProvider::invalidateStatistics );
+      connect( vl, &QgsVectorLayer::updatedFields, this, [ = ] { createVirtualTable( vl, layer.name() ); } );
     }
     else
     {
@@ -302,8 +303,7 @@ bool QgsVirtualLayerProvider::createIt()
     QString vname = mLayers.at( i ).name;
     if ( vlayer )
     {
-      QString createStr = QStringLiteral( "DROP TABLE IF EXISTS \"%1\"; CREATE VIRTUAL TABLE \"%1\" USING QgsVLayer(%2);" ).arg( vname, vlayer->id() );
-      Sqlite::Query::exec( mSqlite.get(), createStr );
+      createVirtualTable( vlayer, vname );
     }
     else
     {
@@ -455,6 +455,12 @@ bool QgsVirtualLayerProvider::createIt()
   return true;
 }
 
+void QgsVirtualLayerProvider::createVirtualTable( QgsVectorLayer *vlayer, const QString &vname )
+{
+  QString createStr = QStringLiteral( "DROP TABLE IF EXISTS \"%1\"; CREATE VIRTUAL TABLE \"%1\" USING QgsVLayer(%2);" ).arg( vname, vlayer->id() );
+  Sqlite::Query::exec( mSqlite.get(), createStr );
+}
+
 bool QgsVirtualLayerProvider::cancelReload()
 {
   return mSqlite.interrupt();

src/providers/virtual/qgsvirtuallayerprovider.h

@@ -111,11 +111,13 @@ class QgsVirtualLayerProvider: public QgsVectorDataProvider
     bool openIt();
     bool createIt();
     bool loadSourceLayers();
+    void createVirtualTable( QgsVectorLayer *vlayer, const QString &name );
 
     friend class QgsVirtualLayerFeatureSource;
 
   private slots:
     void invalidateStatistics();
+
 };
 
 // clazy:excludeall=qstring-allocations

tests/src/python/test_provider_virtual.py

@@ -977,6 +977,40 @@ def testFiltersWithoutUid(self):
 
         QgsProject.instance().removeMapLayer(ml)
 
+    def testUpdatedFields(self):
+        """Test when referenced layer update its fields
+        https://issues.qgis.org/issues/20893
+        """
+
+        ml = QgsVectorLayer("Point?srid=EPSG:4326&field=a:int", "mem", "memory")
+        self.assertEqual(ml.isValid(), True)
+        QgsProject.instance().addMapLayer(ml)
+
+        ml.startEditing()
+        f1 = QgsFeature(ml.fields())
+        f1.setGeometry(QgsGeometry.fromWkt('POINT(2 3)'))
+        ml.addFeatures([f1])
+        ml.commitChanges()
+
+        vl = QgsVectorLayer("?query=select a, geometry from mem", "vl", "virtual")
+        self.assertEqual(vl.isValid(), True)
+
+        # add one more field
+        ml.dataProvider().addAttributes([QgsField('newfield', QVariant.Int)])
+        ml.updateFields()
+
+        self.assertEqual(ml.featureCount(), vl.featureCount())
+        self.assertEqual(vl.fields().count(), 1)
+
+        geometry = next(vl.getFeatures()).geometry()
+        self.assertTrue(geometry)
+
+        point = geometry.asPoint()
+        self.assertEqual(point.x(), 2)
+        self.assertEqual(point.y(), 3)
+
+        QgsProject.instance().removeMapLayer(ml)
+
 
 if __name__ == '__main__':
     unittest.main()