[FEATURE] New class QgsJSONUtils with utilities for converting

features to and from GeoJSON strings

Sponsored by Kanton of Zug, Switzerland

python/core/core.sip

@@ -57,6 +57,7 @@
 %Include qgsgml.sip
 %Include qgsgmlschema.sip
 %Include qgshistogram.sip
+%Include qgsjsonutils.sip
 %Include qgsmaptopixelgeometrysimplifier.sip
 %Include qgstransaction.sip
 %Include qgstransactiongroup.sip

python/core/qgsjsonutils.sip

@@ -0,0 +1,58 @@
+/** \ingroup core
+ * \class QgsJSONUtils
+ * \brief Helper utilities for working with JSON and GeoJSON conversions.
+ * \note Added in version 2.16
+ */
+
+class QgsJSONUtils
+{
+%TypeHeaderCode
+#include <qgsjsonutils.h>
+%End
+
+  public:
+
+    /** Attempts to parse a GeoJSON string to a collection of features.
+     * @param string GeoJSON string to parse
+     * @param fields fields collection to use for parsed features
+     * @param encoding text encoding
+     * @returns list of parsed features, or an empty list if no features could be parsed
+     * @see stringToFields()
+     * @note this function is a wrapper around QgsOgrUtils::stringToFeatureList()
+     */
+    static QgsFeatureList stringToFeatureList( const QString& string, const QgsFields& fields, QTextCodec* encoding );
+
+    /** Attempts to retrieve the fields from a GeoJSON string representing a collection of features.
+     * @param string GeoJSON string to parse
+     * @param encoding text encoding
+     * @returns retrieved fields collection, or an empty list if no fields could be determined from the string
+     * @see stringToFeatureList()
+     * @note this function is a wrapper around QgsOgrUtils::stringToFields()
+     */
+    static QgsFields stringToFields( const QString& string, QTextCodec* encoding );
+
+    /** Returns a GeoJSON string representation of a feature.
+     * @param feature feature to convert
+     * @param precision maximum number of decimal places to use for geometry coordinates
+     * @param attrIndexes list of attribute indexes to include in GeoJSON, or an empty list to include
+     * all attributes
+     * @param includeGeom set to false to avoid including the geometry representation in the JSON output
+     * @param includeAttributes set to false to avoid including any attribute values in the JSON output
+     * @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
+     */
+    static QString featureToGeoJSON( const QgsFeature& feature,
+                                     int precision = 17,
+                                     const QgsAttributeList& attrIndexes = QgsAttributeList(),
+                                     bool includeGeom = true,
+                                     bool includeAttributes = true,
+                                     const QVariant& id = QVariant() );
+
+    /** Encodes a value to a JSON string representation, adding appropriate quotations and escaping
+     * where required.
+     * @param value value to encode
+     * @returns encoded value
+     */
+    static QString encodeValue( const QVariant& value );
+};

src/core/CMakeLists.txt

@@ -121,6 +121,7 @@ SET(QGIS_CORE_SRCS
   qgsgml.cpp
   qgsgmlschema.cpp
   qgshistogram.cpp
+  qgsjsonutils.cpp
   qgslabel.cpp
   qgslabelattributes.cpp
   qgslabelfeature.cpp
@@ -636,6 +637,7 @@ SET(QGIS_CORE_HDRS
   qgsgeometrycache.h
   qgshistogram.h
   qgsindexedfeature.h
+  qgsjsonutils.h
   qgslayerdefinition.h
   qgslabel.h
   qgslabelattributes.h

src/core/qgsjsonutils.cpp

@@ -0,0 +1,121 @@
+/***************************************************************************
+    qgsjsonutils.h
+     -------------
+    Date                 : May 206
+    Copyright            : (C) 2016 Nyall Dawson
+    Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsjsonutils.h"
+#include "qgsogrutils.h"
+#include "qgsgeometry.h"
+
+QgsFeatureList QgsJSONUtils::stringToFeatureList( const QString &string, const QgsFields &fields, QTextCodec *encoding )
+{
+  return QgsOgrUtils::stringToFeatureList( string, fields, encoding );
+}
+
+QgsFields QgsJSONUtils::stringToFields( const QString &string, QTextCodec *encoding )
+{
+  return QgsOgrUtils::stringToFields( string, encoding );
+}
+
+QString QgsJSONUtils::featureToGeoJSON( const QgsFeature& feature,
+                                        int precision,
+                                        const QgsAttributeList& attrIndexes,
+                                        bool includeGeom,
+                                        bool includeAttributes,
+                                        const QVariant& id )
+{
+  QString s = "{\n   \"type\":\"Feature\",\n";
+
+  // ID
+  s += QString( "   \"id\":%1" ).arg( !id.isValid() ? QString::number( feature.id() ) : encodeValue( id ) );
+
+  if ( includeAttributes || includeGeom )
+    s += ",\n";
+  else
+    s += '\n';
+
+  const QgsGeometry* geom = feature.constGeometry();
+  if ( geom && !geom->isEmpty() && includeGeom )
+  {
+    QgsRectangle box = geom->boundingBox();
+
+    if ( QgsWKBTypes::flatType( geom->geometry()->wkbType() ) != QgsWKBTypes::Point )
+    {
+      s += QString( "   \"bbox\":[%1, %2, %3, %4],\n" ).arg( qgsDoubleToString( box.xMinimum(), precision ),
+           qgsDoubleToString( box.yMinimum(), precision ),
+           qgsDoubleToString( box.xMaximum(), precision ),
+           qgsDoubleToString( box.yMaximum(), precision ) );
+    }
+    s += "   \"geometry\":\n   ";
+    s += geom->exportToGeoJSON( precision );
+    if ( includeAttributes )
+      s += ",\n";
+    else
+      s += '\n';
+  }
+
+  if ( includeAttributes )
+  {
+    //read all attribute values from the feature
+    s += "   \"properties\":{\n";
+
+    const QgsFields* fields = feature.fields();
+    int attributeCounter = 0;
+
+    for ( int i = 0; i < fields->count(); ++i )
+    {
+      if ( !attrIndexes.isEmpty() && !attrIndexes.contains( i ) )
+        continue;
+
+      if ( attributeCounter > 0 )
+        s += ",\n";
+      QVariant val =  feature.attributes().at( i );
+
+      s += QString( "      \"%1\":%2" ).arg( fields->at( i ).name(), encodeValue( val ) );
+
+      ++attributeCounter;
+    }
+
+    s += "\n   }\n";
+  }
+
+  s += "}";
+
+  return s;
+}
+
+QString QgsJSONUtils::encodeValue( const QVariant &value )
+{
+  if ( value.isNull() )
+    return "null";
+
+  switch ( value.type() )
+  {
+    case QVariant::Int:
+    case QVariant::UInt:
+    case QVariant::LongLong:
+    case QVariant::ULongLong:
+    case QVariant::Double:
+      return value.toString();
+
+    case QVariant::Bool:
+      return value.toBool() ? "true" : "false";
+
+    default:
+    case QVariant::String:
+      QString v = value.toString().replace( '"', "\\\"" )
+                  .replace( '\r', "\\r" )
+                  .replace( '\n', "\\n" );
+      return v.prepend( '"' ).append( '"' );
+  }
+}

src/core/qgsjsonutils.h

@@ -0,0 +1,79 @@
+/***************************************************************************
+    qgsjsonutils.h
+     -------------
+    Date                 : May 206
+    Copyright            : (C) 2016 Nyall Dawson
+    Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSJSONUTILS_H
+#define QGSJSONUTILS_H
+
+#include "qgsfeature.h"
+
+class QTextCodec;
+
+/** \ingroup core
+ * \class QgsJSONUtils
+ * \brief Helper utilities for working with JSON and GeoJSON conversions.
+ * \note Added in version 2.16
+ */
+
+class CORE_EXPORT QgsJSONUtils
+{
+  public:
+
+    /** Attempts to parse a GeoJSON string to a collection of features.
+     * @param string GeoJSON string to parse
+     * @param fields fields collection to use for parsed features
+     * @param encoding text encoding
+     * @returns list of parsed features, or an empty list if no features could be parsed
+     * @see stringToFields()
+     * @note this function is a wrapper around QgsOgrUtils::stringToFeatureList()
+     */
+    static QgsFeatureList stringToFeatureList( const QString& string, const QgsFields& fields, QTextCodec* encoding );
+
+    /** Attempts to retrieve the fields from a GeoJSON string representing a collection of features.
+     * @param string GeoJSON string to parse
+     * @param encoding text encoding
+     * @returns retrieved fields collection, or an empty list if no fields could be determined from the string
+     * @see stringToFeatureList()
+     * @note this function is a wrapper around QgsOgrUtils::stringToFields()
+     */
+    static QgsFields stringToFields( const QString& string, QTextCodec* encoding );
+
+    /** Returns a GeoJSON string representation of a feature.
+     * @param feature feature to convert
+     * @param precision maximum number of decimal places to use for geometry coordinates
+     * @param attrIndexes list of attribute indexes to include in GeoJSON, or an empty list to include
+     * all attributes
+     * @param includeGeom set to false to avoid including the geometry representation in the JSON output
+     * @param includeAttributes set to false to avoid including any attribute values in the JSON output
+     * @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
+     */
+    static QString featureToGeoJSON( const QgsFeature& feature,
+                                     int precision = 17,
+                                     const QgsAttributeList& attrIndexes = QgsAttributeList(),
+                                     bool includeGeom = true,
+                                     bool includeAttributes = true,
+                                     const QVariant& id = QVariant() );
+
+    /** Encodes a value to a JSON string representation, adding appropriate quotations and escaping
+     * where required.
+     * @param value value to encode
+     * @returns encoded value
+     */
+    static QString encodeValue( const QVariant& value );
+
+};
+
+#endif // QGSJSONUTILS_H

src/server/qgswfsserver.cpp

@@ -38,6 +38,7 @@
 #include "qgsrequesthandler.h"
 #include "qgsogcutils.h"
 #include "qgsaccesscontrol.h"
+#include "qgsjsonutils.h"
 
 #include <QImage>
 #include <QPainter>
@@ -1865,42 +1866,30 @@ QgsFeatureIds QgsWFSServer::getFeatureIdsFromFilter( const QDomElement& filterEl
 
 QString QgsWFSServer::createFeatureGeoJSON( QgsFeature* feat, int prec, QgsCoordinateReferenceSystem &, const QgsAttributeList& attrIndexes, const QSet<QString>& excludedAttributes ) /*const*/
 {
-  QString fStr = "{\"type\": \"Feature\",\n";
-
-  fStr += "   \"id\": ";
-  fStr += "\"" + mTypeName + "." + QString::number( feat->id() ) + "\"";
-  fStr += ",\n";
+  QString id = QString( "%1.%2" ).arg( mTypeName, FID_TO_STRING( feat->id() ) );
 
+  //copy feature so we can modify its geometry as required
+  QgsFeature f( *feat );
   const QgsGeometry* geom = feat->constGeometry();
+  bool withGeom = false;
   if ( geom && mWithGeom && mGeometryName != "NONE" )
   {
-    QgsRectangle box = geom->boundingBox();
-
-    fStr += " \"bbox\": [ " + qgsDoubleToString( box.xMinimum(), prec ) + ", " + qgsDoubleToString( box.yMinimum(), prec ) + ", " + qgsDoubleToString( box.xMaximum(), prec ) + ", " + qgsDoubleToString( box.yMaximum(), prec ) + "],\n";
-
-    fStr += "  \"geometry\": ";
+    withGeom = true;
     if ( mGeometryName == "EXTENT" )
     {
+      QgsRectangle box = geom->boundingBox();
       QgsGeometry* bbox = QgsGeometry::fromRect( box );
-      fStr += bbox->exportToGeoJSON( prec );
-      delete bbox;
+      f.setGeometry( bbox );
     }
     else if ( mGeometryName == "CENTROID" )
     {
       QgsGeometry* centroid = geom->centroid();
-      fStr += centroid->exportToGeoJSON( prec );
-      delete centroid;
+      f.setGeometry( centroid );
     }
-    else
-      fStr += geom->exportToGeoJSON( prec );
-    fStr += ",\n";
   }
 
-  //read all attribute values from the feature
-  fStr += "   \"properties\": {\n";
-  QgsAttributes featureAttributes = feat->attributes();
   const QgsFields* fields = feat->fields();
-  int attributeCounter = 0;
+  QgsAttributeList attrsToExport;
   for ( int i = 0; i < attrIndexes.count(); ++i )
   {
     int idx = attrIndexes[i];
@@ -1914,36 +1903,13 @@ QString QgsWFSServer::createFeatureGeoJSON( QgsFeature* feat, int prec, QgsCoord
     {
       continue;
     }
-    QVariant val = featureAttributes[idx];
 
-    if ( attributeCounter == 0 )
-      fStr += "    \"";
-    else
-      fStr += "   ,\"";
-    fStr += attributeName;
-    fStr += "\": ";
-    if ( val.type() == 6 || val.type() == 2 )
-    {
-      fStr +=  val.toString();
-    }
-    else
-    {
-      fStr += "\"";
-      fStr +=  val.toString()
-               .replace( '"', "\\\"" )
-               .replace( '\r', "\\r" )
-               .replace( '\n', "\\n" );
-      fStr += "\"";
-    }
-    fStr += "\n";
-    ++attributeCounter;
+    attrsToExport << idx;
   }
 
-  fStr += "   }\n";
-
-  fStr += "  }";
+  bool withAttributes = !attrsToExport.isEmpty();
 
-  return fStr;
+  return QgsJSONUtils::featureToGeoJSON( f, prec, attrsToExport, withGeom, withAttributes, id );
 }
 
 QDomElement QgsWFSServer::createFeatureGML2( QgsFeature* feat, QDomDocument& doc, int prec, QgsCoordinateReferenceSystem& crs, const QgsAttributeList& attrIndexes, const QSet<QString>& excludedAttributes ) /*const*/

tests/src/python/CMakeLists.txt

@@ -41,6 +41,7 @@ ADD_PYTHON_TEST(PyQgsGeometryAvoidIntersections test_qgsgeometry_avoid_intersect
 ADD_PYTHON_TEST(PyQgsGeometryGeneratorSymbolLayerV2 test_qgsgeometrygeneratorsymbollayerv2.py)
 ADD_PYTHON_TEST(PyQgsGeometryTest test_qgsgeometry.py)
 ADD_PYTHON_TEST(PyQgsGraduatedSymbolRendererV2 test_qgsgraduatedsymbolrendererv2.py)
+ADD_PYTHON_TEST(PyQgsJSONUtils test_qgsjsonutils.py)
 ADD_PYTHON_TEST(PyQgsMapUnitScale test_qgsmapunitscale.py)
 ADD_PYTHON_TEST(PyQgsMemoryProvider test_provider_memory.py)
 ADD_PYTHON_TEST(PyQgsMultiEditToolButton test_qgsmultiedittoolbutton.py)