Add layer dependencies for virtual layers

Author: Hugo Mercier

src/providers/virtual/qgsvirtuallayerprovider.cpp

@@ -600,6 +600,17 @@ QgsAttributeList QgsVirtualLayerProvider::pkAttributeIndexes()
   return QgsAttributeList();
 }
 
+QSet<QString> QgsVirtualLayerProvider::layerDependencies() const
+{
+  QSet<QString> deps;
+  foreach ( const QgsVirtualLayerDefinition::SourceLayer& l, mDefinition.sourceLayers() )
+  {
+    if ( l.isReferenced() )
+      deps << l.reference();
+  }
+  return deps;
+}
+
 /**
  * Class factory to return a pointer to a newly created
  * QgsSpatiaLiteProvider object

src/providers/virtual/qgsvirtuallayerprovider.h

@@ -89,6 +89,9 @@ class QgsVirtualLayerProvider: public QgsVectorDataProvider
     /** Return list of indexes of fields that make up the primary key */
     QgsAttributeList pkAttributeIndexes() override;
 
+    /** Get the list of layer ids on which this layer depends */
+    QSet<QString> layerDependencies() const override;
+
   private:
 
     // file on disk

tests/src/python/test_provider_virtual.py

@@ -30,6 +30,7 @@
                        QgsProviderRegistry,
                        QgsVirtualLayerDefinition,
                        QgsWKBTypes
+                       QgsProject
                        )
 
 from utilities import (unitTestDataPath,
@@ -664,5 +665,43 @@ def test_queryOnMemoryLayer(self):
         ml.addFeatures([f3])
         self.assertEqual(ml.featureCount(), vl.featureCount())
 
+    def test_ProjectDependencies(self):
+        # make a virtual layer with living references and save it to a project
+        l1 = QgsVectorLayer(os.path.join(self.testDataDir, "france_parts.shp"), "france_parts", "ogr", False)
+        self.assertEqual(l1.isValid(), True)
+        QgsMapLayerRegistry.instance().addMapLayer(l1)
+
+        query = QUrl.toPercentEncoding("SELECT * FROM france_parts")
+        l2 = QgsVectorLayer("?query=%s" % query, "aa", "virtual", False)
+        self.assertEqual(l2.isValid(), True)
+        QgsMapLayerRegistry.instance().addMapLayer(l2)
+
+        self.assertEqual(len(l2.layerDependencies()), 1)
+        self.assertEqual(l2.layerDependencies()[0].startswith('france_parts'), True)
+
+        query = QUrl.toPercentEncoding("SELECT t1.objectid, t2.name_0 FROM france_parts as t1, aa as t2")
+        l3 = QgsVectorLayer("?query=%s" % query, "bb", "virtual", False)
+        self.assertEqual(l3.isValid(), True)
+        QgsMapLayerRegistry.instance().addMapLayer(l3)
+
+        self.assertEqual(len(l2.layerDependencies()), 1)
+        self.assertEqual(l2.layerDependencies()[0].startswith('france_parts'), True)
+
+        self.assertEqual(len(l3.layerDependencies()), 2)
+
+        temp = os.path.join(tempfile.gettempdir(), "qgstestproject.qgs")
+
+        QgsProject.instance().setFileName(temp)
+        QgsProject.instance().write()
+
+        QgsMapLayerRegistry.instance().removeMapLayers([l1, l2])
+        QgsProject.instance().clear()
+
+        QgsProject.instance().setFileName(temp)
+        QgsProject.instance().read()
+
+        # make sure the 3 layers are loaded back
+        self.assertEqual(len(QgsMapLayerRegistry.instance().mapLayers()), 3)
+
 if __name__ == '__main__':
     unittest.main()