Add method to match feature attributes to the given fields

nyalldawson · nyalldawson · commit a8794001e018 · 2018-09-25T08:49:21.000+10:00
Refs #18784
diff --git a/python/core/auto_generated/qgsvectorlayerutils.sip.in b/python/core/auto_generated/qgsvectorlayerutils.sip.in
@@ -156,6 +156,16 @@ The duplicated feature will be automatically inserted into the layer.
 .. versionadded:: 3.0
 %End
 
+
+    static void matchAttributesToFields( QgsFeature &feature, const QgsFields &fields );
+%Docstring
+Matches the attributes in ``feature`` to the specified ``fields``.
+
+This causes the attributes contained within the given ``feature`` to be rearranged (or in
+some cases dropped) in order to match the fields and order indicated by ``fields``.
+
+.. versionadded:: 3.4
+%End
 };
 
 
diff --git a/src/core/qgsvectorlayerutils.cpp b/src/core/qgsvectorlayerutils.cpp
@@ -522,6 +522,44 @@ std::unique_ptr<QgsVectorLayerFeatureSource> QgsVectorLayerUtils::getFeatureSour
   return featureSource;
 }
 
+void QgsVectorLayerUtils::matchAttributesToFields( QgsFeature &feature, const QgsFields &fields )
+{
+  if ( !feature.fields().isEmpty() )
+  {
+    QgsAttributes attributes;
+    attributes.reserve( fields.size() );
+    // feature has a field mapping, so we can match attributes to field names
+    for ( const QgsField &field : fields )
+    {
+      int index = feature.fields().lookupField( field.name() );
+      attributes.append( index >= 0 ? feature.attribute( index ) : QVariant( field.type() ) );
+    }
+    feature.setAttributes( attributes );
+  }
+  else
+  {
+    // no field name mapping in feature, just use order
+    const int lengthDiff = feature.attributes().count() - fields.count();
+    if ( lengthDiff > 0 )
+    {
+      // truncate extra attributes
+      QgsAttributes attributes = feature.attributes().mid( 0, fields.count() );
+      feature.setAttributes( attributes );
+    }
+    else if ( lengthDiff < 0 )
+    {
+      // add missing null attributes
+      QgsAttributes attributes = feature.attributes();
+      attributes.reserve( fields.count() );
+      for ( int i = feature.attributes().count(); i < fields.count(); ++i )
+      {
+        attributes.append( QVariant( fields.at( i ).type() ) );
+      }
+      feature.setAttributes( attributes );
+    }
+  }
+}
+
 QList<QgsVectorLayer *> QgsVectorLayerUtils::QgsDuplicateFeatureContext::layers() const
 {
   QList<QgsVectorLayer *> layers;
diff --git a/src/core/qgsvectorlayerutils.h b/src/core/qgsvectorlayerutils.h
@@ -167,6 +167,16 @@ class CORE_EXPORT QgsVectorLayerUtils
      * \since QGIS 3.4
      */
     static std::unique_ptr<QgsVectorLayerFeatureSource> getFeatureSource( QPointer<QgsVectorLayer> layer ) SIP_SKIP;
+
+    /**
+     * Matches the attributes in \a feature to the specified \a fields.
+     *
+     * This causes the attributes contained within the given \a feature to be rearranged (or in
+     * some cases dropped) in order to match the fields and order indicated by \a fields.
+     *
+     * \since QGIS 3.4
+     */
+    static void matchAttributesToFields( QgsFeature &feature, const QgsFields &fields );
 };
 
 
