Create QgsVectorLayerSelectedFeatureSource

...which is a QgsFeatureSource subclass which only considers
selected features from a QgsVectorLayer

Author: nyalldawson

python/core/qgsvectorlayerfeatureiterator.sip

@@ -46,6 +46,13 @@ class QgsVectorLayerFeatureSource : QgsAbstractFeatureSource
  :rtype: QgsFields
 %End
 
+    QgsCoordinateReferenceSystem crs() const;
+%Docstring
+ Returns the coordinate reference system for features retrieved from this source.
+.. versionadded:: 3.0
+ :rtype: QgsCoordinateReferenceSystem
+%End
+
   protected:
 
 
@@ -138,6 +145,35 @@ Setup the simplification of geometries to fetch using the specified simplify met
     QgsVectorLayerFeatureIterator( const QgsVectorLayerFeatureIterator &rhs );
 };
 
+
+
+class QgsVectorLayerSelectedFeatureSource : QgsFeatureSource
+{
+%Docstring
+ QgsFeatureSource subclass for the selected features from a QgsVectorLayer.
+.. versionadded:: 3.0
+%End
+
+%TypeHeaderCode
+#include "qgsvectorlayerfeatureiterator.h"
+%End
+  public:
+
+    QgsVectorLayerSelectedFeatureSource( QgsVectorLayer *layer );
+%Docstring
+ Constructor for QgsVectorLayerSelectedFeatureSource, for selected features from the specified ``layer``.
+ The currently selected feature IDs are stored, so change to the layer selection after constructing
+ the QgsVectorLayerSelectedFeatureSource will not be reflected.
+%End
+
+    virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest &request = QgsFeatureRequest() ) const;
+    virtual QgsCoordinateReferenceSystem sourceCrs() const;
+    virtual QgsFields fields() const;
+    virtual QgsWkbTypes::Type wkbType() const;
+    virtual long featureCount() const;
+
+};
+
 /************************************************************************
  * This file has been generated automatically from                      *
  *                                                                      *

src/core/qgsvectorlayerfeatureiterator.cpp

@@ -98,6 +98,11 @@ QgsFields QgsVectorLayerFeatureSource::fields() const
   return mFields;
 }
 
+QgsCoordinateReferenceSystem QgsVectorLayerFeatureSource::crs() const
+{
+  return mCrs;
+}
+
 
 QgsVectorLayerFeatureIterator::QgsVectorLayerFeatureIterator( QgsVectorLayerFeatureSource *source, bool ownSource, const QgsFeatureRequest &request )
   : QgsAbstractFeatureIteratorFromSource<QgsVectorLayerFeatureSource>( source, ownSource, request )
@@ -1006,3 +1011,51 @@ bool QgsVectorLayerFeatureIterator::prepareOrderBy( const QList<QgsFeatureReques
   return true;
 }
 
+
+//
+// QgsVectorLayerSelectedFeatureSource
+//
+
+QgsVectorLayerSelectedFeatureSource::QgsVectorLayerSelectedFeatureSource( QgsVectorLayer *layer )
+  : mSource( layer )
+  , mSelectedFeatureIds( layer->selectedFeatureIds() )
+  , mWkbType( layer->wkbType() )
+{}
+
+QgsFeatureIterator QgsVectorLayerSelectedFeatureSource::getFeatures( const QgsFeatureRequest &request ) const
+{
+  QgsFeatureRequest req( request );
+
+  if ( req.filterFids().isEmpty() && req.filterType() != QgsFeatureRequest::FilterFids )
+  {
+    req.setFilterFids( mSelectedFeatureIds );
+  }
+  else if ( !req.filterFids().isEmpty() )
+  {
+    QgsFeatureIds reqIds = mSelectedFeatureIds;
+    reqIds.intersect( req.filterFids() );
+    req.setFilterFids( reqIds );
+  }
+
+  return mSource.getFeatures( req );
+}
+
+QgsCoordinateReferenceSystem QgsVectorLayerSelectedFeatureSource::sourceCrs() const
+{
+  return mSource.crs();
+}
+
+QgsFields QgsVectorLayerSelectedFeatureSource::fields() const
+{
+  return mSource.fields();
+}
+
+QgsWkbTypes::Type QgsVectorLayerSelectedFeatureSource::wkbType() const
+{
+  return mWkbType;
+}
+
+long QgsVectorLayerSelectedFeatureSource::featureCount() const
+{
+  return mSelectedFeatureIds.count();
+}

src/core/qgsvectorlayerfeatureiterator.h

@@ -20,6 +20,7 @@
 #include "qgsfeatureiterator.h"
 #include "qgsfields.h"
 #include "qgscoordinatereferencesystem.h"
+#include "qgsfeaturesource.h"
 
 #include <QSet>
 #include <memory>
@@ -67,6 +68,12 @@ class CORE_EXPORT QgsVectorLayerFeatureSource : public QgsAbstractFeatureSource
      */
     QgsFields fields() const;
 
+    /**
+     * Returns the coordinate reference system for features retrieved from this source.
+     * \since QGIS 3.0
+     */
+    QgsCoordinateReferenceSystem crs() const;
+
   protected:
 
     QgsAbstractFeatureSource *mProviderFeatureSource = nullptr;
@@ -253,4 +260,38 @@ class CORE_EXPORT QgsVectorLayerFeatureIterator : public QgsAbstractFeatureItera
     bool checkGeometryValidity( const QgsFeature &feature );
 };
 
+
+
+/**
+ * \class QgsVectorLayerSelectedFeatureSource
+ * \ingroup core
+ * QgsFeatureSource subclass for the selected features from a QgsVectorLayer.
+ * \since QGIS 3.0
+ */
+class CORE_EXPORT QgsVectorLayerSelectedFeatureSource : public QgsFeatureSource
+{
+  public:
+
+    /**
+     * Constructor for QgsVectorLayerSelectedFeatureSource, for selected features from the specified \a layer.
+     * The currently selected feature IDs are stored, so change to the layer selection after constructing
+     * the QgsVectorLayerSelectedFeatureSource will not be reflected.
+     */
+    QgsVectorLayerSelectedFeatureSource( QgsVectorLayer *layer );
+
+    virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest &request = QgsFeatureRequest() ) const override;
+    virtual QgsCoordinateReferenceSystem sourceCrs() const override;
+    virtual QgsFields fields() const override;
+    virtual QgsWkbTypes::Type wkbType() const override;
+    virtual long featureCount() const override;
+
+  private:
+
+    // ideally this wouldn't be mutable, but QgsVectorLayerFeatureSource has non-const getFeatures()
+    mutable QgsVectorLayerFeatureSource mSource;
+    QgsFeatureIds mSelectedFeatureIds;
+    QgsWkbTypes::Type mWkbType = QgsWkbTypes::Unknown;
+
+};
+
 #endif // QGSVECTORLAYERFEATUREITERATOR_H

tests/src/python/test_qgsvectorlayer.py

@@ -52,6 +52,7 @@
                        QgsSingleCategoryDiagramRenderer,
                        QgsDiagramLayerSettings,
                        QgsTextFormat,
+                       QgsVectorLayerSelectedFeatureSource,
                        NULL)
 from qgis.testing import start_app, unittest
 from featuresourcetestbase import FeatureSourceTestCase
@@ -2298,6 +2299,61 @@ def testClone(self):
         # compare xml documents
         self.assertEqual(layer_doc.toString(), clone_doc.toString())
 
+    def testQgsVectorLayerSelectedFeatureSource(self):
+        """
+        test QgsVectorLayerSelectedFeatureSource
+        """
+
+        layer = QgsVectorLayer("Point?crs=epsg:3111&field=fldtxt:string&field=fldint:integer",
+                               "addfeat", "memory")
+        pr = layer.dataProvider()
+        f1 = QgsFeature(1)
+        f1.setAttributes(["test", 123])
+        f1.setGeometry(QgsGeometry.fromPoint(QgsPointXY(100, 200)))
+        f2 = QgsFeature(2)
+        f2.setAttributes(["test2", 457])
+        f2.setGeometry(QgsGeometry.fromPoint(QgsPointXY(200, 200)))
+        f3 = QgsFeature(3)
+        f3.setAttributes(["test2", 888])
+        f3.setGeometry(QgsGeometry.fromPoint(QgsPointXY(300, 200)))
+        f4 = QgsFeature(4)
+        f4.setAttributes(["test3", -1])
+        f4.setGeometry(QgsGeometry.fromPoint(QgsPointXY(400, 300)))
+        f5 = QgsFeature(5)
+        f5.setAttributes(["test4", 0])
+        f5.setGeometry(QgsGeometry.fromPoint(QgsPointXY(0, 0)))
+        self.assertTrue(pr.addFeatures([f1, f2, f3, f4, f5]))
+        self.assertEqual(layer.featureCount(), 5)
+
+        source = QgsVectorLayerSelectedFeatureSource(layer)
+        self.assertEqual(source.sourceCrs().authid(), 'EPSG:3111')
+        self.assertEqual(source.wkbType(), QgsWkbTypes.Point)
+        self.assertEqual(source.fields(), layer.fields())
+
+        # no selection
+        self.assertEqual(source.featureCount(), 0)
+        it = source.getFeatures()
+        f = QgsFeature()
+        self.assertFalse(it.nextFeature(f))
+
+        # with selection
+        layer.selectByIds([f1.id(), f3.id(), f5.id()])
+        source = QgsVectorLayerSelectedFeatureSource(layer)
+        self.assertEqual(source.featureCount(), 3)
+        ids = set([f.id() for f in source.getFeatures()])
+        self.assertEqual(ids, {f1.id(), f3.id(), f5.id()})
+
+        # test that source has stored snapshot of selected features
+        layer.selectByIds([f2.id(), f4.id()])
+        self.assertEqual(source.featureCount(), 3)
+        ids = set([f.id() for f in source.getFeatures()])
+        self.assertEqual(ids, {f1.id(), f3.id(), f5.id()})
+
+        # test that source is not dependent on layer
+        del layer
+        ids = set([f.id() for f in source.getFeatures()])
+        self.assertEqual(ids, {f1.id(), f3.id(), f5.id()})
+
 
 # TODO:
 # - fetch rect: feat with changed geometry: 1. in rect, 2. out of rect