Merge pull request #4491 from nyalldawson/proxy_sink

Add QgsProxyFeatureSink

Author: nyalldawson

python/core/qgsfeaturesink.sip

@@ -49,6 +49,43 @@ class QgsFeatureSink
 
 };
 
+
+class QgsProxyFeatureSink : QgsFeatureSink
+{
+%Docstring
+ A simple feature sink which proxies feature addition on to another feature sink.
+
+ This class is designed to allow factory methods which always return new QgsFeatureSink
+ objects. Since it is not always possible to create an entirely new QgsFeatureSink
+ (e.g. if the feature sink is a layer's data provider), a new QgsProxyFeatureSink
+ can instead be returned which forwards features on to the destination sink. The
+ proxy sink can be safely deleted without affecting the destination sink.
+
+.. versionadded:: 3.0
+%End
+
+%TypeHeaderCode
+#include "qgsfeaturesink.h"
+%End
+  public:
+
+    QgsProxyFeatureSink( QgsFeatureSink *sink );
+%Docstring
+ Constructs a new QgsProxyFeatureSink which forwards features onto a destination ``sink``.
+%End
+    virtual bool addFeature( QgsFeature &feature );
+    virtual bool addFeatures( QgsFeatureList &features );
+    virtual bool addFeatures( QgsFeatureIterator &iterator );
+
+    QgsFeatureSink *destinationSink();
+%Docstring
+ Returns the destination QgsFeatureSink which the proxy will forward features to.
+ :rtype: QgsFeatureSink
+%End
+
+};
+
+
 /************************************************************************
  * This file has been generated automatically from                      *
  *                                                                      *

python/core/qgsfeaturestore.sip

@@ -58,6 +58,22 @@ Constructor
     virtual bool addFeatures( QgsFeatureList &features );
 
 
+    int count() const;
+%Docstring
+ Returns the number of features contained in the store.
+ :rtype: int
+%End
+
+
+    int __len__() const;
+%Docstring
+ Returns the number of features contained in the store.
+ :rtype: int
+%End
+%MethodCode
+    sipRes = sipCpp->count();
+%End
+
     QgsFeatureList features() const;
 %Docstring
  Returns the list of features contained in the store.

src/core/qgsfeaturesink.cpp

@@ -39,3 +39,7 @@ bool QgsFeatureSink::addFeatures( QgsFeatureIterator &iterator )
   return result;
 }
 
+
+QgsProxyFeatureSink::QgsProxyFeatureSink( QgsFeatureSink *sink )
+  : mSink( sink )
+{}

src/core/qgsfeaturesink.h

@@ -58,4 +58,41 @@ class CORE_EXPORT QgsFeatureSink
 
 };
 
+
+/**
+ * \class QgsProxyFeatureSink
+ * \ingroup core
+ * A simple feature sink which proxies feature addition on to another feature sink.
+ *
+ * This class is designed to allow factory methods which always return new QgsFeatureSink
+ * objects. Since it is not always possible to create an entirely new QgsFeatureSink
+ * (e.g. if the feature sink is a layer's data provider), a new QgsProxyFeatureSink
+ * can instead be returned which forwards features on to the destination sink. The
+ * proxy sink can be safely deleted without affecting the destination sink.
+ *
+ * \since QGIS 3.0
+ */
+class CORE_EXPORT QgsProxyFeatureSink : public QgsFeatureSink
+{
+  public:
+
+    /**
+     * Constructs a new QgsProxyFeatureSink which forwards features onto a destination \a sink.
+     */
+    QgsProxyFeatureSink( QgsFeatureSink *sink );
+    bool addFeature( QgsFeature &feature ) override { return mSink->addFeature( feature ); }
+    bool addFeatures( QgsFeatureList &features ) override { return mSink->addFeatures( features ); }
+    bool addFeatures( QgsFeatureIterator &iterator ) override { return mSink->addFeatures( iterator ); }
+
+    /**
+     * Returns the destination QgsFeatureSink which the proxy will forward features to.
+     */
+    QgsFeatureSink *destinationSink() { return mSink; }
+
+  private:
+
+    QgsFeatureSink *mSink;
+};
+
+
 #endif // QGSFEATURESINK_H

src/core/qgsfeaturestore.h

@@ -64,6 +64,22 @@ class CORE_EXPORT QgsFeatureStore : public QgsFeatureSink
     bool addFeature( QgsFeature &feature ) override;
     bool addFeatures( QgsFeatureList &features ) override;
 
+    /**
+     * Returns the number of features contained in the store.
+     */
+    int count() const { return mFeatures.size(); }
+
+#ifdef SIP_RUN
+
+    /**
+     * Returns the number of features contained in the store.
+     */
+    int __len__() const;
+    % MethodCode
+    sipRes = sipCpp->count();
+    % End
+#endif
+
     /**
      * Returns the list of features contained in the store.
      */

tests/src/python/test_qgsfeaturesink.py

@@ -19,7 +19,12 @@
                        QgsVectorLayer,
                        QgsFeature,
                        QgsGeometry,
-                       QgsPoint)
+                       QgsPoint,
+                       QgsField,
+                       QgsFields,
+                       QgsCoordinateReferenceSystem,
+                       QgsProxyFeatureSink)
+from qgis.PyQt.QtCore import QVariant
 from qgis.testing import start_app, unittest
 start_app()
 
@@ -62,6 +67,35 @@ def testFromIterator(self):
         vals = [f['fldint'] for f in store.features()]
         self.assertEqual(vals, [123, 457, 888, -1, 0])
 
+    def testProxyFeatureSink(self):
+        fields = QgsFields()
+        fields.append(QgsField('fldtxt', QVariant.String))
+        fields.append(QgsField('fldint', QVariant.Int))
+
+        store = QgsFeatureStore(fields, QgsCoordinateReferenceSystem())
+        proxy = QgsProxyFeatureSink(store)
+        self.assertEqual(proxy.destinationSink(), store)
+
+        self.assertEqual(len(store), 0)
+
+        f = QgsFeature()
+        f.setAttributes(["test", 123])
+        f.setGeometry(QgsGeometry.fromPoint(QgsPoint(100, 200)))
+        proxy.addFeature(f)
+        self.assertEqual(len(store), 1)
+        self.assertEqual(store.features()[0]['fldtxt'], 'test')
+
+        f2 = QgsFeature()
+        f2.setAttributes(["test2", 457])
+        f2.setGeometry(QgsGeometry.fromPoint(QgsPoint(200, 200)))
+        f3 = QgsFeature()
+        f3.setAttributes(["test3", 888])
+        f3.setGeometry(QgsGeometry.fromPoint(QgsPoint(300, 200)))
+        proxy.addFeatures([f2, f3])
+        self.assertEqual(len(store), 3)
+        self.assertEqual(store.features()[1]['fldtxt'], 'test2')
+        self.assertEqual(store.features()[2]['fldtxt'], 'test3')
+
 
 if __name__ == '__main__':
     unittest.main()