Use QJson for JSON encoding of features

python/core/auto_generated/qgsjsonutils.sip.in

@@ -228,6 +228,22 @@ Returns a GeoJSON string representation of a feature.
 
 :return: GeoJSON string
 
+.. seealso:: :py:func:`exportFeatures`
+%End
+
+    QJsonObject exportFeatureV2( const QgsFeature &feature,
+                                 const QVariantMap &extraProperties = QVariantMap(),
+                                 const QVariant &id = QVariant() ) const;
+%Docstring
+Returns a GeoJSON string representation of a feature.
+
+:param feature: feature to convert
+:param extraProperties: map of extra attributes to include in feature's properties
+:param id: optional ID to use as GeoJSON feature's ID instead of input feature's ID. If omitted, feature's
+           ID is used.
+
+:return: GeoJSON string
+
 .. seealso:: :py:func:`exportFeatures`
 %End
 
@@ -314,6 +330,19 @@ Exports all attributes from a QgsFeature as a JSON map type.
                               to speed up exporting the attributes for multiple features from the same layer.
 %End
 
+    static QJsonObject exportAttributesV2( const QgsFeature &feature, QgsVectorLayer *layer = 0,
+                                           const QVector<QVariant> &attributeWidgetCaches = QVector<QVariant>() );
+%Docstring
+Exports all attributes from a QgsFeature as a JSON map type.
+
+:param feature: feature to export
+:param layer: optional associated vector layer. If specified, this allows
+              richer export utilising settings like the layer's fields widget configuration.
+:param attributeWidgetCaches: optional widget configuration cache. Can be used
+                              to speed up exporting the attributes for multiple features from the same layer.
+%End
+
+
     static QVariantList parseArray( const QString &json, QVariant::Type type );
 %Docstring
 Parse a simple array (depth=1).

src/core/qgsjsonutils.cpp

@@ -236,6 +236,136 @@ QString QgsJsonExporter::exportFeature( const QgsFeature &feature, const QVarian
   return s;
 }
 
+QJsonObject QgsJsonExporter::exportFeatureV2( const QgsFeature &feature, const QVariantMap &extraProperties, const QVariant &id ) const
+{
+  QJsonObject featureJson
+  {
+    { QStringLiteral( "type" ), QStringLiteral( "Feature" ) },
+    { QStringLiteral( "id" ), ( ! id.isValid() ? QJsonValue( feature.id() ) : QJsonValue::fromVariant( id ) )  },
+  };
+
+  QgsGeometry geom = feature.geometry();
+  if ( !geom.isNull() && mIncludeGeometry )
+  {
+    if ( mCrs.isValid() )
+    {
+      try
+      {
+        QgsGeometry transformed = geom;
+        if ( transformed.transform( mTransform ) == 0 )
+          geom = transformed;
+      }
+      catch ( QgsCsException &cse )
+      {
+        Q_UNUSED( cse );
+      }
+    }
+    QgsRectangle box = geom.boundingBox();
+
+    if ( QgsWkbTypes::flatType( geom.wkbType() ) != QgsWkbTypes::Point )
+    {
+      featureJson[ QStringLiteral( "bbox" ) ] = QJsonArray( { qgsDoubleToString( box.xMinimum(), mPrecision ),
+          qgsDoubleToString( box.yMinimum(), mPrecision ),
+          qgsDoubleToString( box.xMaximum(), mPrecision ),
+          qgsDoubleToString( box.yMaximum(), mPrecision ) } );
+    }
+    featureJson[ QStringLiteral( "geometry" ) ] =  QJsonDocument::fromJson( geom.asJson( mPrecision ).toLocal8Bit() ).object();
+  }
+  else
+  {
+    featureJson[ QStringLiteral( "geometry" ) ] = QJsonValue();
+  }
+
+  // build up properties element
+  int attributeCounter { 0 };
+  QJsonObject properties;
+  if ( mIncludeAttributes || !extraProperties.isEmpty() )
+  {
+    //read all attribute values from the feature
+    if ( mIncludeAttributes )
+    {
+      QgsFields fields = mLayer ? mLayer->fields() : feature.fields();
+      // List of formatters through we want to pass the values
+      QStringList formattersWhiteList;
+      formattersWhiteList << QStringLiteral( "KeyValue" )
+                          << QStringLiteral( "List" )
+                          << QStringLiteral( "ValueRelation" )
+                          << QStringLiteral( "ValueMap" );
+
+      for ( int i = 0; i < fields.count(); ++i )
+      {
+        if ( ( !mAttributeIndexes.isEmpty() && !mAttributeIndexes.contains( i ) ) || mExcludedAttributeIndexes.contains( i ) )
+          continue;
+
+        QVariant val = feature.attributes().at( i );
+
+        if ( mLayer )
+        {
+          QgsEditorWidgetSetup setup = fields.at( i ).editorWidgetSetup();
+          QgsFieldFormatter *fieldFormatter = QgsApplication::fieldFormatterRegistry()->fieldFormatter( setup.type() );
+          if ( formattersWhiteList.contains( fieldFormatter->id() ) )
+            val = fieldFormatter->representValue( mLayer.data(), i, setup.config(), QVariant(), val );
+        }
+
+        QString name = fields.at( i ).name();
+        if ( mAttributeDisplayName )
+        {
+          name = mLayer->attributeDisplayName( i );
+        }
+        properties[ name ] = QJsonValue::fromVariant( val );
+        attributeCounter++;
+      }
+    }
+
+    if ( !extraProperties.isEmpty() )
+    {
+      QVariantMap::const_iterator it = extraProperties.constBegin();
+      for ( ; it != extraProperties.constEnd(); ++it )
+      {
+        properties[ it.key() ] = QJsonValue::fromVariant( it.value() );
+        attributeCounter++;
+      }
+    }
+
+    // related attributes
+    if ( mLayer && mIncludeRelatedAttributes )
+    {
+      QList< QgsRelation > relations = QgsProject::instance()->relationManager()->referencedRelations( mLayer.data() );
+      for ( const auto &relation : qgis::as_const( relations ) )
+      {
+        QgsFeatureRequest req = relation.getRelatedFeaturesRequest( feature );
+        req.setFlags( QgsFeatureRequest::NoGeometry );
+        QgsVectorLayer *childLayer = relation.referencingLayer();
+        QJsonArray relatedFeatureAttributes;
+        if ( childLayer )
+        {
+          QgsFeatureIterator it = childLayer->getFeatures( req );
+          QVector<QVariant> attributeWidgetCaches;
+          int fieldIndex = 0;
+          const QgsFields fields { childLayer->fields() };
+          for ( const QgsField &field : fields )
+          {
+            QgsEditorWidgetSetup setup = field.editorWidgetSetup();
+            QgsFieldFormatter *fieldFormatter = QgsApplication::fieldFormatterRegistry()->fieldFormatter( setup.type() );
+            attributeWidgetCaches.append( fieldFormatter->createCache( childLayer, fieldIndex, setup.config() ) );
+            fieldIndex++;
+          }
+          QgsFeature relatedFet;
+          while ( it.nextFeature( relatedFet ) )
+          {
+            relatedFeatureAttributes += QgsJsonUtils::exportAttributes( relatedFet, childLayer, attributeWidgetCaches );
+          }
+        }
+        properties[ relation.name() ] = relatedFeatureAttributes;
+        attributeCounter++;
+      }
+    }
+  }
+  // bool hasProperties = attributeCounter > 0;
+  featureJson[ QStringLiteral( "properties" ) ] = properties;
+  return featureJson;
+}
+
 QString QgsJsonExporter::exportFeatures( const QgsFeatureList &features ) const
 {
   QStringList featureJSON;
@@ -244,7 +374,6 @@ QString QgsJsonExporter::exportFeatures( const QgsFeatureList &features ) const
   {
     featureJSON << exportFeature( feature );
   }
-
   return QStringLiteral( "{ \"type\": \"FeatureCollection\",\n    \"features\":[\n%1\n]}" ).arg( featureJSON.join( QStringLiteral( ",\n" ) ) );
 }
 
@@ -351,3 +480,25 @@ QVariantList QgsJsonUtils::parseArray( const QString &json, QVariant::Type type
   }
   return result;
 }
+
+
+QJsonObject QgsJsonUtils::exportAttributesV2( const QgsFeature &feature, QgsVectorLayer *layer, const QVector<QVariant> &attributeWidgetCaches )
+{
+  QgsFields fields = feature.fields();
+  QJsonObject attrs;
+  for ( int i = 0; i < fields.count(); ++i )
+  {
+    QVariant val = feature.attributes().at( i );
+
+    if ( layer )
+    {
+      QgsEditorWidgetSetup setup = layer->fields().at( i ).editorWidgetSetup();
+      QgsFieldFormatter *fieldFormatter = QgsApplication::fieldFormatterRegistry()->fieldFormatter( setup.type() );
+      if ( fieldFormatter != QgsApplication::fieldFormatterRegistry()->fallbackFieldFormatter() )
+        val = fieldFormatter->representValue( layer, i, setup.config(), attributeWidgetCaches.count() >= i ? attributeWidgetCaches.at( i ) : QVariant(), val );
+    }
+
+    attrs.insert( fields.at( i ).name(), QJsonValue::fromVariant( val ) );
+  }
+  return attrs;
+}

src/core/qgsjsonutils.h

@@ -23,6 +23,7 @@
 #include "qgsfields.h"
 
 #include <QPointer>
+#include <QJsonValue>
 
 class QTextCodec;
 
@@ -198,6 +199,19 @@ class CORE_EXPORT QgsJsonExporter
                            const QVariantMap &extraProperties = QVariantMap(),
                            const QVariant &id = QVariant() ) const;
 
+    /**
+     * Returns a GeoJSON string representation of a feature.
+     * \param feature feature to convert
+     * \param extraProperties map of extra attributes to include in feature's properties
+     * \param id optional ID to use as GeoJSON feature's ID instead of input feature's ID. If omitted, feature's
+     * ID is used.
+     * \returns GeoJSON string
+     * \see exportFeatures()
+     */
+    QJsonObject exportFeatureV2( const QgsFeature &feature,
+                                 const QVariantMap &extraProperties = QVariantMap(),
+                                 const QVariant &id = QVariant() ) const;
+
 
     /**
      * Returns a GeoJSON string representation of a list of features (feature collection).
@@ -291,6 +305,18 @@ class CORE_EXPORT QgsJsonUtils
     static QString exportAttributes( const QgsFeature &feature, QgsVectorLayer *layer = nullptr,
                                      const QVector<QVariant> &attributeWidgetCaches = QVector<QVariant>() );
 
+    /**
+     * Exports all attributes from a QgsFeature as a JSON map type.
+     * \param feature feature to export
+     * \param layer optional associated vector layer. If specified, this allows
+     * richer export utilising settings like the layer's fields widget configuration.
+     * \param attributeWidgetCaches optional widget configuration cache. Can be used
+     * to speed up exporting the attributes for multiple features from the same layer.
+     */
+    static QJsonObject exportAttributesV2( const QgsFeature &feature, QgsVectorLayer *layer = nullptr,
+                                           const QVector<QVariant> &attributeWidgetCaches = QVector<QVariant>() );
+
+
     /**
      * Parse a simple array (depth=1).
      * \param json the JSON to parse

tests/src/core/testqgsjsonutils.cpp

@@ -15,6 +15,9 @@
 
 #include "qgstest.h"
 #include <qgsjsonutils.h>
+#include "qgsvectorlayer.h"
+#include "qgsfeature.h"
+
 
 class TestQgsJsonUtils : public QObject
 {
@@ -71,6 +74,86 @@ class TestQgsJsonUtils : public QObject
       QCOMPARE( back, list );
       QCOMPARE( back.at( 0 ).type(), QVariant::Double );
     }
+
+    void testV2ExportAttributes_data()
+    {
+      QTest::addColumn<bool>( "useQJson" );
+      QTest::newRow( "Use V2 (QJson)" ) << true;
+      QTest::newRow( "Use old string concat" ) << false;
+    }
+
+    void testV2ExportAttributes()
+    {
+
+      QFETCH( bool, useQJson );
+
+      QgsVectorLayer vl { QStringLiteral( "Point?field=fldtxt:string&field=fldint:integer&field=flddbl:double" ), QStringLiteral( "mem" ), QStringLiteral( "memory" ) };
+      QgsFeature feature { vl.fields() };
+      feature.setAttributes( QgsAttributes() << QStringLiteral( "a value" ) << 1 << 2.0 );
+
+      if ( useQJson )  // average: 0.0048 msecs per iteration
+      {
+        QBENCHMARK
+        {
+          const auto json { QgsJsonUtils::exportAttributesV2( feature, &vl ) };
+          QCOMPARE( QJsonDocument( json ).toJson( QJsonDocument::JsonFormat::Compact ), QStringLiteral( "{\"flddbl\":2,\"fldint\":1,\"fldtxt\":\"a value\"}" ) );
+        }
+      }
+      else // average: 0.0070 msecs per iteration
+      {
+        QBENCHMARK
+        {
+          const auto json { QgsJsonUtils::exportAttributes( feature, &vl ) };
+          QCOMPARE( json, QStringLiteral( "{\"fldtxt\":\"a value\",\n\"fldint\":1,\n\"flddbl\":2}" ) );
+        }
+      }
+    }
+
+    void testV2ExportFeature_data()
+    {
+      QTest::addColumn<bool>( "useQJson" );
+      QTest::newRow( "Use V2 (QJson)" ) << true;
+      QTest::newRow( "Use old string concat" ) << false;
+    }
+
+    void testV2ExportFeature()
+    {
+
+      QFETCH( bool, useQJson );
+
+      QgsVectorLayer vl { QStringLiteral( "Polygon?field=fldtxt:string&field=fldint:integer&field=flddbl:double" ), QStringLiteral( "mem" ), QStringLiteral( "memory" ) };
+      QgsFeature feature { vl.fields() };
+      feature.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "POLYGON((1 1,5 1,5 5,1 5,1 1),(2 2, 3 2, 3 3, 2 3,2 2))" ) ) );
+      feature.setAttributes( QgsAttributes() << QStringLiteral( "a value" ) << 1 << 2.0 );
+
+      QgsJsonExporter exporter { &vl };
+
+      if ( useQJson )  // average: 0.063 msecs per iteration
+      {
+        QBENCHMARK
+        {
+          const auto json { exporter.exportFeatureV2( feature ) };
+          QCOMPARE( QJsonDocument( json ).toJson( QJsonDocument::JsonFormat::Compact ),
+                    QStringLiteral( "{\"bbox\":[\"1\",\"1\",\"5\",\"5\"],\"geometry\":{\"coordinates\""
+                                    ":[[[1,1],[5,1],[5,5],[1,5],[1,1]],[[2,2],[3,2],[3,3],[2,3],[2,2]]],"
+                                    "\"type\":\"Polygon\"},\"id\":0,\"properties\":{\"flddbl\":2,\"fldint\":"
+                                    "1,\"fldtxt\":\"a value\"},\"type\":\"Feature\"}"
+                                  ) );
+        }
+      }
+      else // average: 0.047 msecs per iteration
+      {
+        QBENCHMARK
+        {
+          const auto json { exporter.exportFeature( feature ) };
+          QCOMPARE( json, QStringLiteral( "{\n   \"type\":\"Feature\",\n   \"id\":0,\n   \"bbox\":[1, 1, 5, 5],\n   "
+                                          "\"geometry\":\n   {\"type\": \"Polygon\", "
+                                          "\"coordinates\": [[ [1, 1], [5, 1], [5, 5], [1, 5], [1, 1]], [ [2, 2], "
+                                          "[3, 2], [3, 3], [2, 3], [2, 2]]] },\n   "
+                                          "\"properties\":{\n      \"fldtxt\":\"a value\",\n      \"fldint\":1,\n      \"flddbl\":2\n   }\n}" ) );
+        }
+      }
+    }
 };
 
 QGSTEST_MAIN( TestQgsJsonUtils )