Merge pull request #5695 from pblottiere/bugfix_virtuallayer_218

[backport][bugfix] Fixes #16798 FilterFid feature requests with virtual layers

Author: pblottiere

src/providers/virtual/qgsvirtuallayerfeatureiterator.cpp

@@ -37,6 +37,7 @@ QgsVirtualLayerFeatureIterator::QgsVirtualLayerFeatureIterator( QgsVirtualLayerF
     QString tableName = mSource->provider()->mTableName;
 
     QStringList wheres;
+    QString offset;
     QString subset = mSource->provider()->mSubset;
     if ( !subset.isNull() )
     {
@@ -76,6 +77,17 @@ QgsVirtualLayerFeatureIterator::QgsVirtualLayerFeatureIterator( QgsVirtualLayerF
       values += ")";
       wheres << values;
     }
+    else if ( mDefinition.uid().isNull() && request.filterType() == QgsFeatureRequest::FilterFid )
+    {
+      if ( request.filterFid() >= 0 )
+      {
+        offset = QString( " LIMIT 1 OFFSET %1" ).arg( request.filterFid() );
+      }
+      else // never return a feature if the id is negative
+      {
+        offset = QString( " LIMIT 0" );
+      }
+    }
 
     mFields = mSource->provider()->fields();
     if ( request.flags() & QgsFeatureRequest::SubsetOfAttributes )
@@ -111,7 +123,15 @@ QgsVirtualLayerFeatureIterator::QgsVirtualLayerFeatureIterator( QgsVirtualLayerF
       }
       else
       {
-        columns = "0";
+        columns = QString( "0" );
+        if ( request.filterType() == QgsFeatureRequest::FilterFid )
+        {
+          columns = QString::number( request.filterFid() );
+        }
+        else
+        {
+          columns = QString( "0" );
+        }
       }
       Q_FOREACH ( int i, mAttributes )
       {
@@ -134,6 +154,11 @@ QgsVirtualLayerFeatureIterator::QgsVirtualLayerFeatureIterator( QgsVirtualLayerF
       mSqlQuery += " WHERE " + wheres.join( " AND " );
     }
 
+    if ( !offset.isEmpty() )
+    {
+      mSqlQuery += offset;
+    }
+
     mQuery.reset( new Sqlite::Query( mSqlite, mSqlQuery ) );
 
     mFid = 0;
@@ -191,7 +216,8 @@ bool QgsVirtualLayerFeatureIterator::fetchFeature( QgsFeature& feature )
 
   feature.setFields( mFields, /* init */ true );
 
-  if ( mDefinition.uid().isNull() )
+  if ( mDefinition.uid().isNull() &&
+       mRequest.filterType() != QgsFeatureRequest::FilterFid )
   {
     // no id column => autoincrement
     feature.setFeatureId( mFid++ );

tests/src/python/test_provider_virtual.py

@@ -86,6 +86,46 @@ def tearDown(self):
         """Run after each test."""
         pass
 
+    def test_filterfid_crossjoin(self):
+        l0 = QgsVectorLayer(os.path.join(self.testDataDir, "france_parts.shp"), "france_parts", "ogr")
+        self.assertTrue(l0.isValid())
+        QgsMapLayerRegistry.instance().addMapLayer(l0)
+
+        l1 = QgsVectorLayer(os.path.join(self.testDataDir, "points.shp"), "points", "ogr")
+        self.assertTrue(l1.isValid())
+        QgsMapLayerRegistry.instance().addMapLayer(l1)
+
+        # cross join
+        query = QUrl.toPercentEncoding("SELECT * FROM france_parts,points")
+        vl = QgsVectorLayer("?query=%s" % query, "tt", "virtual")
+
+        self.assertEqual(vl.featureCount(), l0.featureCount() * l1.featureCount())
+
+        # test with FilterFid requests
+        f = next(vl.getFeatures(QgsFeatureRequest().setFilterFid(0)))
+        idx = f.fields().fieldNameIndex('Class')
+        self.assertEqual(f.id(), 0)
+        self.assertEqual(f.attributes()[idx], 'Jet')
+
+        f = next(vl.getFeatures(QgsFeatureRequest().setFilterFid(5)))
+        self.assertEqual(f.id(), 5)
+        self.assertEqual(f.attributes()[idx], 'Biplane')
+
+        # test with FilterFid requests
+        fit = vl.getFeatures(QgsFeatureRequest().setFilterFids([0, 3, 5]))
+
+        f = next(fit)
+        self.assertEqual(f.id(), 0)
+        self.assertEqual(f.attributes()[idx], 'Jet')
+
+        f = next(fit)
+        self.assertEqual(f.id(), 3)
+        self.assertEqual(f.attributes()[idx], 'Jet')
+
+        f = next(fit)
+        self.assertEqual(f.id(), 5)
+        self.assertEqual(f.attributes()[idx], 'Biplane')
+
     def test_CsvNoGeometry(self):
         l1 = QgsVectorLayer(QUrl.fromLocalFile(os.path.join(self.testDataDir, "delimitedtext/test.csv")).toString() + "?type=csv&geomType=none&subsetIndex=no&watchFile=no", "test", "delimitedtext", False)
         self.assertEqual(l1.isValid(), True)