Support including attributes of related (child) features in

GeoJSON feature export

Sponsored by Kanton of Zug, Switzerland

python/core/qgsjsonutils.sip

@@ -12,11 +12,10 @@ class QgsJSONExporter
   public:
 
     /** Constructor for QgsJSONExporter.
+     * @param vectorLayer associated vector layer (required for related attribute export)
      * @param precision maximum number of decimal places to use for geometry coordinates
-     * @param includeGeometry 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
      */
-    QgsJSONExporter( int precision = 17, bool includeGeometry = true, bool includeAttributes = true );
+    QgsJSONExporter( const QgsVectorLayer* vectorLayer = nullptr, int precision = 17 );
 
     /** Sets the maximum number of decimal places to use in geometry coordinates.
      * @param precision number of decimal places
@@ -51,6 +50,30 @@ class QgsJSONExporter
      */
     bool includeAttributes() const;
 
+    /** Sets whether to include attributes of features linked via references in the JSON exports.
+     * @param includeRelated set to true to include attributes for any related child features
+     * within the exported properties element.
+     * @note associated vector layer must be set with setVectorLayer()
+     * @see includeRelated()
+     */
+    void setIncludeRelated( bool includeRelated );
+
+    /** Returns whether attributes of related (child) features will be included in the JSON exports.
+     * @see setIncludeRelated()
+     */
+    bool includeRelated() const;
+
+    /** Sets the associated vector layer (required for related attribute export).
+     * @param vectorLayer vector layer
+     * @see vectorLayer()
+     */
+    void setVectorLayer( const QgsVectorLayer* vectorLayer );
+
+    /** Returns the associated vector layer, if set.
+     * @see setVectorLayer()
+     */
+    QgsVectorLayer* vectorLayer() const;
+
     /** Sets the list of attributes to include in the JSON exports.
      * @param attributes list of attribute indexes, or an empty list to include all
      * attributes
@@ -138,4 +161,9 @@ class QgsJSONUtils
      * @returns encoded value
      */
     static QString encodeValue( const QVariant& value );
+
+    /** Exports all attributes from a QgsFeature as a JSON map type.
+     * @param feature feature to export
+     */
+    static QString exportAttributes( const QgsFeature& feature );
 };

src/core/qgsjsonutils.cpp

@@ -16,16 +16,32 @@
 #include "qgsjsonutils.h"
 #include "qgsogrutils.h"
 #include "qgsgeometry.h"
+#include "qgsvectorlayer.h"
+#include "qgsmaplayerregistry.h"
+#include "qgsrelation.h"
+#include "qgsrelationmanager.h"
+#include "qgsproject.h"
 
-
-QgsJSONExporter::QgsJSONExporter( int precision, bool includeGeometry, bool includeAttributes )
+QgsJSONExporter::QgsJSONExporter( const QgsVectorLayer* vectorLayer, int precision )
     : mPrecision( precision )
-    , mIncludeGeometry( includeGeometry )
-    , mIncludeAttributes( includeAttributes )
+    , mIncludeGeometry( true )
+    , mIncludeAttributes( true )
+    , mIncludeRelatedAttributes( false )
+    , mLayerId( vectorLayer ? vectorLayer->id() : QString() )
 {
 
 }
 
+void QgsJSONExporter::setVectorLayer( const QgsVectorLayer* vectorLayer )
+{
+  mLayerId = vectorLayer ? vectorLayer->id() : QString();
+}
+
+QgsVectorLayer *QgsJSONExporter::vectorLayer() const
+{
+  return qobject_cast< QgsVectorLayer* >( QgsMapLayerRegistry::instance()->mapLayer( mLayerId ) );
+}
+
 QString QgsJSONExporter::exportFeature( const QgsFeature& feature, const QVariantMap& extraProperties,
                                         const QVariant& id ) const
 {
@@ -37,7 +53,6 @@ QString QgsJSONExporter::exportFeature( const QgsFeature& feature, const QVarian
   {
     //read all attribute values from the feature
 
-
     if ( mIncludeAttributes )
     {
       const QgsFields* fields = feature.fields();
@@ -70,7 +85,43 @@ QString QgsJSONExporter::exportFeature( const QgsFeature& feature, const QVarian
         ++attributeCounter;
       }
     }
+
+    // related attributes
+    QgsVectorLayer* vl = vectorLayer();
+    if ( vl && mIncludeRelatedAttributes )
+    {
+      QList< QgsRelation > relations = QgsProject::instance()->relationManager()->referencedRelations( vl );
+      Q_FOREACH ( const QgsRelation& relation, relations )
+      {
+        if ( attributeCounter > 0 )
+          properties += ",\n";
+
+        QgsFeatureRequest req = relation.getRelatedFeaturesRequest( feature );
+        req.setFlags( QgsFeatureRequest::NoGeometry );
+        QgsVectorLayer* childLayer = relation.referencingLayer();
+        QString relatedFeatureAttributes;
+        if ( childLayer )
+        {
+          QgsFeatureIterator it = childLayer->getFeatures( req );
+          QgsFeature relatedFet;
+          int relationFeatures = 0;
+          while ( it.nextFeature( relatedFet ) )
+          {
+            if ( relationFeatures > 0 )
+              relatedFeatureAttributes += ",\n";
+
+            relatedFeatureAttributes += QgsJSONUtils::exportAttributes( relatedFet );
+            relationFeatures++;
+          }
+        }
+        relatedFeatureAttributes.prepend( '[' ).append( ']' );
+
+        properties += QString( "      \"%1\":%2" ).arg( relation.name(), relatedFeatureAttributes );
+        attributeCounter++;
+      }
+    }
   }
+
   bool hasProperties = attributeCounter > 0;
 
   QString s = "{\n   \"type\":\"Feature\",\n";
@@ -115,6 +166,7 @@ QString QgsJSONExporter::exportFeature( const QgsFeature& feature, const QVarian
 }
 
 
+
 //
 // QgsJSONUtils
 //
@@ -194,3 +246,19 @@ QString QgsJSONUtils::encodeValue( const QVariant &value )
       return v.prepend( '"' ).append( '"' );
   }
 }
+
+QString QgsJSONUtils::exportAttributes( const QgsFeature& feature )
+{
+  const QgsFields* fields = feature.fields();
+  QString attrs;
+  for ( int i = 0; i < fields->count(); ++i )
+  {
+    if ( i > 0 )
+      attrs += ",\n";
+
+    QVariant val = feature.attributes().at( i );
+    attrs += encodeValue( fields->at( i ).name() ) + ':' + encodeValue( val );
+  }
+  return attrs.prepend( '{' ).append( '}' );
+}
+

src/core/qgsjsonutils.h

@@ -19,6 +19,7 @@
 #include "qgsfeature.h"
 
 class QTextCodec;
+class QgsVectorLayer;
 
 /** \ingroup core
  * \class QgsJSONExporter
@@ -31,11 +32,10 @@ class CORE_EXPORT QgsJSONExporter
   public:
 
     /** Constructor for QgsJSONExporter.
+     * @param vectorLayer associated vector layer (required for related attribute export)
      * @param precision maximum number of decimal places to use for geometry coordinates
-     * @param includeGeometry 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
      */
-    QgsJSONExporter( int precision = 17, bool includeGeometry = true, bool includeAttributes = true );
+    QgsJSONExporter( const QgsVectorLayer* vectorLayer = nullptr, int precision = 17 );
 
     /** Sets the maximum number of decimal places to use in geometry coordinates.
      * @param precision number of decimal places
@@ -70,6 +70,30 @@ class CORE_EXPORT QgsJSONExporter
      */
     bool includeAttributes() const { return mIncludeAttributes; }
 
+    /** Sets whether to include attributes of features linked via references in the JSON exports.
+     * @param includeRelated set to true to include attributes for any related child features
+     * within the exported properties element.
+     * @note associated vector layer must be set with setVectorLayer()
+     * @see includeRelated()
+     */
+    void setIncludeRelated( bool includeRelated ) { mIncludeRelatedAttributes = includeRelated; }
+
+    /** Returns whether attributes of related (child) features will be included in the JSON exports.
+     * @see setIncludeRelated()
+     */
+    bool includeRelated() const { return mIncludeRelatedAttributes; }
+
+    /** Sets the associated vector layer (required for related attribute export).
+     * @param vectorLayer vector layer
+     * @see vectorLayer()
+     */
+    void setVectorLayer( const QgsVectorLayer* vectorLayer );
+
+    /** Returns the associated vector layer, if set.
+     * @see setVectorLayer()
+     */
+    QgsVectorLayer* vectorLayer() const;
+
     /** Sets the list of attributes to include in the JSON exports.
      * @param attributes list of attribute indexes, or an empty list to include all
      * attributes
@@ -115,6 +139,7 @@ class CORE_EXPORT QgsJSONExporter
                            const QVariantMap& extraProperties = QVariantMap(),
                            const QVariant& id = QVariant() ) const;
 
+
   private:
 
     //! Maximum number of decimal places for geometry coordinates
@@ -133,6 +158,12 @@ class CORE_EXPORT QgsJSONExporter
     //! Whether to include attributes in JSON export
     bool mIncludeAttributes;
 
+    //! Whether to include attributes from related features in JSON export
+    bool mIncludeRelatedAttributes;
+
+    //! Layer ID of associated vector layer. Required for related attribute export.
+    QString mLayerId;
+
 };
 
 /** \ingroup core
@@ -171,6 +202,11 @@ class CORE_EXPORT QgsJSONUtils
      */
     static QString encodeValue( const QVariant& value );
 
+    /** Exports all attributes from a QgsFeature as a JSON map type.
+     * @param feature feature to export
+     */
+    static QString exportAttributes( const QgsFeature& feature );
+
 };
 
 #endif // QGSJSONUTILS_H