Move uniqueValues to QgsFeatureSource

Also change signature of QgsVectorLayer/QgsVectorDataProvider
uniqueValues method to match (and improve API)

doc/api_break.dox

@@ -2275,6 +2275,7 @@ clause fragment which must be evaluated by the provider in order to calculate th
 QGIS 3.0 defaultValue() only returns literal, constant defaultValues. A new method defaultValueClause
 has been added which returns the SQL clause fragments which must be evaluated by the provider itself.
 - isSaveAndLoadStyleToDBSupported() was renamed to isSaveAndLoadStyleToDatabaseSupported()
+- The c++ signature for uniqueValues() has changed (the PyQGIS method remains unchanged)
 
 
 QgsVectorJoinInfo   {#qgis_api_break_3_0_QgsVectorJoinInfo}
@@ -2335,6 +2336,7 @@ displayExpression instead. For the map tip use mapTipTemplate() instead.
 - addFeatures() no longer accepts a makeSelected boolean, and will not automatically select newly added features. If desired, features must be manually selected by calling selectByIds() after addFeatures()
 - annotationForm() and setAnnotationForm() have been removed. Form path is stored in individual QgsFormAnnotation objects.
 - setLayerTransparency, layerTransparency, and layerTransparencyChanged were removed. Use opacity, setOpacity and opacityChanged instead.
+- The c++ signature for uniqueValues() has changed (the PyQGIS method remains unchanged)
 
 
 QgsVectorLayerEditBuffer        {#qgis_api_break_3_0_QgsVectorLayerEditBuffer}

python/core/qgsfeaturesource.sip

@@ -69,6 +69,15 @@ class QgsFeatureSource
  :rtype: long
 %End
 
+    virtual QSet<QVariant> uniqueValues( int fieldIndex, int limit = -1 ) const;
+%Docstring
+ Returns the set of unique values contained within the specified ``fieldIndex`` from this source.
+ If specified, the ``limit`` option can be used to limit the number of returned values.
+ The base class implementation uses a non-optimised approach of looping through
+ all features in the source.
+ :rtype: set of QVariant
+%End
+
 };
 
 

python/core/qgsvectordataprovider.sip

@@ -156,16 +156,6 @@ Bitmask of all provider's editing capabilities
  :rtype: QVariant
 %End
 
-    virtual void uniqueValues( int index, QList<QVariant> &uniqueValues /Out/, int limit = -1 ) const;
-%Docstring
- Return unique values of an attribute
- \param index the index of the attribute
- \param uniqueValues values reference to the list to fill
- \param limit maxmum number of the values to return
-
- Default implementation simply iterates the features
-%End
-
     virtual QStringList uniqueStringsMatching( int index, const QString &substring, int limit = -1,
         QgsFeedback *feedback = 0 ) const;
 %Docstring

python/core/qgsvectorlayer.sip

@@ -1507,18 +1507,19 @@ Assembles mUpdatedFields considering provider fields, joined fields and added fi
  :rtype: QgsEditorWidgetSetup
 %End
 
-    void uniqueValues( int index, QList<QVariant> &uniqueValues /Out/, int limit = -1 ) const;
+    virtual QSet<QVariant> uniqueValues( int fieldIndex, int limit = -1 ) const;
+
 %Docstring
  Calculates a list of unique values contained within an attribute in the layer. Note that
  in some circumstances when unsaved changes are present for the layer then the returned list
  may contain outdated values (for instance when the attribute value in a saved feature has
  been changed inside the edit buffer then the previous saved value will be included in the
  returned list).
- \param index column index for attribute
- \param uniqueValues out: result list
+ \param fieldIndex column index for attribute
  \param limit maximum number of values to return (or -1 if unlimited)
 .. seealso:: minimumValue()
 .. seealso:: maximumValue()
+ :rtype: set of QVariant
 %End
 
     QStringList uniqueStringsMatching( int index, const QString &substring, int limit = -1,

src/core/CMakeLists.txt

@@ -158,6 +158,7 @@ SET(QGIS_CORE_SRCS
   qgsfeatureiterator.cpp
   qgsfeaturerequest.cpp
   qgsfeaturesink.cpp
+  qgsfeaturesource.cpp
   qgsfeaturestore.cpp
   qgsfield.cpp
   qgsfieldconstraints.cpp

src/core/dxf/qgsdxfexport.cpp

@@ -787,8 +787,7 @@ void QgsDxfExport::writeTables()
     }
     else
     {
-      QList<QVariant> values;
-      vl->uniqueValues( attrIdx, values );
+      QSet<QVariant> values = vl->uniqueValues( attrIdx );
       Q_FOREACH ( const QVariant &v, values )
       {
         layerNames << dxfLayerName( v.toString() );

src/core/processing/qgsprocessingutils.cpp

@@ -274,9 +274,8 @@ QList<QVariant> QgsProcessingUtils::uniqueValues( QgsVectorLayer *layer, int fie
   if ( !useSelection )
   {
     // not using selection, so use provider optimised version
-    QList<QVariant> values;
-    layer->uniqueValues( fieldIndex, values );
-    return values;
+    QSet<QVariant> values = layer->uniqueValues( fieldIndex );
+    return values.toList();
   }
   else
   {

src/core/qgis.h

@@ -173,7 +173,7 @@ template<class Object> inline QgsSignalBlocker<Object> whileBlocking( Object *ob
 }
 
 //! Hash for QVariant
-uint qHash( const QVariant &variant );
+CORE_EXPORT uint qHash( const QVariant &variant );
 
 //! Returns a string representation of a double
 //! \param a double value

src/core/qgsfeaturesource.cpp

@@ -0,0 +1,42 @@
+/***************************************************************************
+                         qgsfeaturesource.cpp
+                         -------------------
+    begin                : May 2017
+    copyright            : (C) 2017 by 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 "qgsfeaturesource.h"
+#include "qgsfeaturerequest.h"
+#include "qgsfeatureiterator.h"
+
+QSet<QVariant> QgsFeatureSource::uniqueValues( int fieldIndex, int limit ) const
+{
+  if ( fieldIndex < 0 || fieldIndex >= fields().count() )
+    return QSet<QVariant>();
+
+  QgsFeatureRequest req;
+  req.setFlags( QgsFeatureRequest::NoGeometry );
+  req.setSubsetOfAttributes( QgsAttributeList() << fieldIndex );
+
+  QSet<QVariant> values;
+  QgsFeatureIterator it = getFeatures( req );
+  QgsFeature f;
+  while ( it.nextFeature( f ) )
+  {
+    values.insert( f.attribute( fieldIndex ) );
+    if ( limit > 0 && values.size() >= limit )
+      return values;
+  }
+  return values;
+}
+

src/core/qgsfeaturesource.h

@@ -20,9 +20,9 @@
 
 #include "qgis_core.h"
 #include "qgis.h"
+#include "qgsfeaturerequest.h"
 
 class QgsFeatureIterator;
-class QgsFeatureRequest;
 class QgsCoordinateReferenceSystem;
 class QgsFields;
 
@@ -79,6 +79,14 @@ class CORE_EXPORT QgsFeatureSource
      */
     virtual long featureCount() const = 0;
 
+    /**
+     * Returns the set of unique values contained within the specified \a fieldIndex from this source.
+     * If specified, the \a limit option can be used to limit the number of returned values.
+     * The base class implementation uses a non-optimised approach of looping through
+     * all features in the source.
+     */
+    virtual QSet<QVariant> uniqueValues( int fieldIndex, int limit = -1 ) const;
+
 };
 
 Q_DECLARE_METATYPE( QgsFeatureSource * )

src/core/qgsvectordataprovider.cpp

@@ -433,28 +433,6 @@ QVariant QgsVectorDataProvider::maximumValue( int index ) const
   return mCacheMaxValues[index];
 }
 
-void QgsVectorDataProvider::uniqueValues( int index, QList<QVariant> &values, int limit ) const
-{
-  QgsFeature f;
-  QgsAttributeList keys;
-  keys.append( index );
-  QgsFeatureIterator fi = getFeatures( QgsFeatureRequest().setSubsetOfAttributes( keys ).setFlags( QgsFeatureRequest::NoGeometry ) );
-
-  QSet<QString> set;
-  values.clear();
-
-  while ( fi.nextFeature( f ) )
-  {
-    if ( !set.contains( f.attribute( index ).toString() ) )
-    {
-      values.append( f.attribute( index ) );
-      set.insert( f.attribute( index ).toString() );
-    }
-
-    if ( limit >= 0 && values.size() >= limit )
-      break;
-  }
-}
 
 QStringList QgsVectorDataProvider::uniqueStringsMatching( int index, const QString &substring, int limit, QgsFeedback *feedback ) const
 {

src/core/qgsvectordataprovider.h

@@ -186,16 +186,6 @@ class CORE_EXPORT QgsVectorDataProvider : public QgsDataProvider, public QgsFeat
      */
     virtual QVariant maximumValue( int index ) const;
 
-    /**
-     * Return unique values of an attribute
-     * \param index the index of the attribute
-     * \param uniqueValues values reference to the list to fill
-     * \param limit maxmum number of the values to return
-     *
-     * Default implementation simply iterates the features
-     */
-    virtual void uniqueValues( int index, QList<QVariant> &uniqueValues SIP_OUT, int limit = -1 ) const;
-
     /**
      * Returns unique string values of an attribute which contain a specified subset string. Subset
      * matching is done in a case-insensitive manner.

src/core/qgsvectorlayer.cpp

@@ -3010,23 +3010,23 @@ QString QgsVectorLayer::defaultValueExpression( int index ) const
     return mFields.at( index ).defaultValueExpression();
 }
 
-void QgsVectorLayer::uniqueValues( int index, QList<QVariant> &uniqueValues, int limit ) const
+QSet<QVariant> QgsVectorLayer::uniqueValues( int index, int limit ) const
 {
-  uniqueValues.clear();
+  QSet<QVariant> uniqueValues;
   if ( !mDataProvider )
   {
-    return;
+    return uniqueValues;
   }
 
   QgsFields::FieldOrigin origin = mFields.fieldOrigin( index );
   switch ( origin )
   {
     case QgsFields::OriginUnknown:
-      return;
+      return uniqueValues;
 
     case QgsFields::OriginProvider: //a provider field
     {
-      mDataProvider->uniqueValues( index, uniqueValues, limit );
+      uniqueValues = mDataProvider->uniqueValues( index, limit );
 
       if ( mEditBuffer )
       {
@@ -3070,7 +3070,7 @@ void QgsVectorLayer::uniqueValues( int index, QList<QVariant> &uniqueValues, int
         }
       }
 
-      return;
+      return uniqueValues;
     }
 
     case QgsFields::OriginEdit:
@@ -3080,8 +3080,8 @@ void QgsVectorLayer::uniqueValues( int index, QList<QVariant> &uniqueValues, int
            !mEditBuffer->mDeletedAttributeIds.contains( index ) &&
            mEditBuffer->mChangedAttributeValues.isEmpty() )
       {
-        mDataProvider->uniqueValues( index, uniqueValues, limit );
-        return;
+        uniqueValues = mDataProvider->uniqueValues( index, limit );
+        return uniqueValues;
       }
       FALLTHROUGH;
     //we need to go through each feature
@@ -3108,12 +3108,12 @@ void QgsVectorLayer::uniqueValues( int index, QList<QVariant> &uniqueValues, int
         }
       }
 
-      uniqueValues = val.values();
-      return;
+      return val.values().toSet();
     }
   }
 
   Q_ASSERT_X( false, "QgsVectorLayer::uniqueValues()", "Unknown source of the field!" );
+  return uniqueValues;
 }
 
 QStringList QgsVectorLayer::uniqueStringsMatching( int index, const QString &substring, int limit, QgsFeedback *feedback ) const

src/core/qgsvectorlayer.h

@@ -1423,13 +1423,12 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      * may contain outdated values (for instance when the attribute value in a saved feature has
      * been changed inside the edit buffer then the previous saved value will be included in the
      * returned list).
-     * \param index column index for attribute
-     * \param uniqueValues out: result list
+     * \param fieldIndex column index for attribute
      * \param limit maximum number of values to return (or -1 if unlimited)
      * \see minimumValue()
      * \see maximumValue()
      */
-    void uniqueValues( int index, QList<QVariant> &uniqueValues SIP_OUT, int limit = -1 ) const;
+    QSet<QVariant> uniqueValues( int fieldIndex, int limit = -1 ) const override;
 
     /**
      * Returns unique string values of an attribute which contain a specified subset string. Subset

src/gui/editorwidgets/qgsrelationreferencewidget.cpp

@@ -466,13 +466,12 @@ void QgsRelationReferenceWidget::init()
     {
       Q_FOREACH ( const QString &fieldName, mFilterFields )
       {
-        QVariantList uniqueValues;
         int idx = mReferencedLayer->fields().lookupField( fieldName );
         QComboBox *cb = new QComboBox();
         cb->setProperty( "Field", fieldName );
         cb->setProperty( "FieldAlias", mReferencedLayer->attributeDisplayName( idx ) );
         mFilterComboBoxes << cb;
-        mReferencedLayer->uniqueValues( idx, uniqueValues );
+        QVariantList uniqueValues = mReferencedLayer->uniqueValues( idx ).toList();
         cb->addItem( mReferencedLayer->attributeDisplayName( idx ) );
         QVariant nullValue = QgsApplication::nullRepresentation();
         cb->addItem( nullValue.toString(), QVariant( mReferencedLayer->fields().at( idx ).type() ) );

src/gui/editorwidgets/qgsuniquevaluewidgetwrapper.cpp

@@ -61,9 +61,7 @@ void QgsUniqueValuesWidgetWrapper::initWidget( QWidget *editor )
 
   QStringList sValues;
 
-  QList<QVariant> values;
-
-  layer()->uniqueValues( fieldIdx(), values );
+  QSet< QVariant> values = layer()->uniqueValues( fieldIdx() );
 
   Q_FOREACH ( const QVariant &v, values )
   {

src/gui/qgsexpressionbuilderwidget.cpp

@@ -336,9 +336,8 @@ void QgsExpressionBuilderWidget::fillFieldValues( const QString &fieldName, int
   if ( fieldIndex < 0 )
     return;
 
-  QList<QVariant> values;
   QStringList strValues;
-  mLayer->uniqueValues( fieldIndex, values, countLimit );
+  QSet<QVariant> values = mLayer->uniqueValues( fieldIndex, countLimit );
   Q_FOREACH ( const QVariant &value, values )
   {
     QString strValue;

src/gui/qgsquerybuilder.cpp

@@ -117,29 +117,27 @@ void QgsQueryBuilder::fillValues( int idx, int limit )
   mModelValues->clear();
 
   // determine the field type
-  QList<QVariant> values;
-  mLayer->uniqueValues( idx, values, limit );
+  QSet<QVariant> values = mLayer->uniqueValues( idx, limit );
 
-  QgsSettings settings;
   QString nullValue = QgsApplication::nullRepresentation();
 
   QgsDebugMsg( QString( "nullValue: %1" ).arg( nullValue ) );
 
-  for ( int i = 0; i < values.size(); i++ )
+  Q_FOREACH ( const QVariant &var, values )
   {
     QString value;
-    if ( values[i].isNull() )
+    if ( var.isNull() )
       value = nullValue;
-    else if ( values[i].type() == QVariant::Date && mLayer->providerType() == QLatin1String( "ogr" ) && mLayer->storageType() == QLatin1String( "ESRI Shapefile" ) )
-      value = values[i].toDate().toString( QStringLiteral( "yyyy/MM/dd" ) );
+    else if ( var.type() == QVariant::Date && mLayer->providerType() == QLatin1String( "ogr" ) && mLayer->storageType() == QLatin1String( "ESRI Shapefile" ) )
+      value = var.toDate().toString( QStringLiteral( "yyyy/MM/dd" ) );
     else
-      value = values[i].toString();
+      value = var.toString();
 
     QStandardItem *myItem = new QStandardItem( value );
     myItem->setEditable( false );
-    myItem->setData( values[i], Qt::UserRole + 1 );
+    myItem->setData( var, Qt::UserRole + 1 );
     mModelValues->insertRow( mModelValues->rowCount(), myItem );
-    QgsDebugMsg( QString( "Value is null: %1\nvalue: %2" ).arg( values[i].isNull() ).arg( values[i].isNull() ? nullValue : values[i].toString() ) );
+    QgsDebugMsg( QString( "Value is null: %1\nvalue: %2" ).arg( var.isNull() ).arg( var.isNull() ? nullValue : var.toString() ) );
   }
 }
 

src/gui/symbology-ng/qgscategorizedsymbolrendererwidget.cpp

@@ -649,7 +649,7 @@ void QgsCategorizedSymbolRendererWidget::addCategories()
   }
   else
   {
-    mLayer->uniqueValues( idx, unique_vals );
+    unique_vals = mLayer->uniqueValues( idx ).toList();
   }
 
   // ask to abort if too many classes

src/providers/mssql/qgsmssqlprovider.cpp

@@ -607,9 +607,9 @@ QVariant QgsMssqlProvider::maximumValue( int index ) const
 }
 
 // Returns the list of unique values of an attribute
-void QgsMssqlProvider::uniqueValues( int index, QList<QVariant> &uniqueValues, int limit ) const
+QSet<QVariant> QgsMssqlProvider::uniqueValues( int index, int limit ) const
 {
-  uniqueValues.clear();
+  QSet<QVariant> uniqueValues;
 
   // get the field name
   QgsField fld = mAttributeFields.at( index );
@@ -643,9 +643,10 @@ void QgsMssqlProvider::uniqueValues( int index, QList<QVariant> &uniqueValues, i
     // read all features
     while ( query.next() )
     {
-      uniqueValues.append( query.value( 0 ) );
+      uniqueValues.insert( query.value( 0 ) );
     }
   }
+  return uniqueValues;
 }
 
 

src/providers/mssql/qgsmssqlprovider.h

@@ -66,7 +66,7 @@ class QgsMssqlProvider : public QgsVectorDataProvider
     virtual QStringList subLayers() const override;
     virtual QVariant minimumValue( int index ) const override;
     virtual QVariant maximumValue( int index ) const override;
-    virtual void uniqueValues( int index, QList<QVariant> &uniqueValues, int limit = -1 ) const override;
+    virtual QSet<QVariant> uniqueValues( int index, int limit = -1 ) const override;
     virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest &request ) const override;
 
     virtual QgsWkbTypes::Type wkbType() const override;

src/providers/ogr/qgsogrprovider.cpp

@@ -30,6 +30,8 @@ email                : sherman at mrcc.com
 #include "qgsgeometry.h"
 #include "qgscoordinatereferencesystem.h"
 #include "qgsvectorlayerexporter.h"
+#include "qgis.h"
+
 
 #define CPL_SUPRESS_CPLUSPLUS  //#spellok
 #include <gdal.h>         // to collect version information
@@ -2949,17 +2951,17 @@ QgsCoordinateReferenceSystem QgsOgrProvider::crs() const
   return srs;
 }
 
-void QgsOgrProvider::uniqueValues( int index, QList<QVariant> &uniqueValues, int limit ) const
+QSet<QVariant> QgsOgrProvider::uniqueValues( int index, int limit ) const
 {
-  uniqueValues.clear();
+  QSet<QVariant> uniqueValues;
 
   if ( !mValid || index < 0 || index >= mAttributeFields.count() )
-    return;
+    return uniqueValues;
 
   QgsField fld = mAttributeFields.at( index );
   if ( fld.name().isNull() )
   {
-    return; //not a provider field
+    return uniqueValues; //not a provider field
   }
 
   QByteArray sql = "SELECT DISTINCT " + quotedIdentifier( textEncoding()->fromUnicode( fld.name() ) );
@@ -2977,7 +2979,7 @@ void QgsOgrProvider::uniqueValues( int index, QList<QVariant> &uniqueValues, int
   if ( !l )
   {
     QgsDebugMsg( "Failed to execute SQL" );
-    return QgsVectorDataProvider::uniqueValues( index, uniqueValues, limit );
+    return QgsVectorDataProvider::uniqueValues( index, limit );
   }
 
   OGRFeatureH f;
@@ -2991,6 +2993,7 @@ void QgsOgrProvider::uniqueValues( int index, QList<QVariant> &uniqueValues, int
   }
 
   OGR_DS_ReleaseResultSet( ogrDataSource, l );
+  return uniqueValues;
 }
 
 QStringList QgsOgrProvider::uniqueStringsMatching( int index, const QString &substring, int limit, QgsFeedback *feedback ) const

src/providers/ogr/qgsogrprovider.h

@@ -103,7 +103,7 @@ class QgsOgrProvider : public QgsVectorDataProvider
     bool isValid() const override;
     QVariant minimumValue( int index ) const override;
     QVariant maximumValue( int index ) const override;
-    virtual void uniqueValues( int index, QList<QVariant> &uniqueValues, int limit = -1 ) const override;
+    virtual QSet< QVariant > uniqueValues( int index, int limit = -1 ) const override;
     virtual QStringList uniqueStringsMatching( int index, const QString &substring, int limit = -1,
         QgsFeedback *feedback = nullptr ) const override;
 

src/providers/postgres/qgspostgresprovider.cpp

@@ -1553,9 +1553,9 @@ QVariant QgsPostgresProvider::minimumValue( int index ) const
 }
 
 // Returns the list of unique values of an attribute
-void QgsPostgresProvider::uniqueValues( int index, QList<QVariant> &uniqueValues, int limit ) const
+QSet<QVariant> QgsPostgresProvider::uniqueValues( int index, int limit ) const
 {
-  uniqueValues.clear();
+  QSet<QVariant> uniqueValues;
 
   try
   {
@@ -1583,12 +1583,13 @@ void QgsPostgresProvider::uniqueValues( int index, QList<QVariant> &uniqueValues
     if ( res.PQresultStatus() == PGRES_TUPLES_OK )
     {
       for ( int i = 0; i < res.PQntuples(); i++ )
-        uniqueValues.append( convertValue( fld.type(), fld.subType(), res.PQgetvalue( i, 0 ) ) );
+        uniqueValues.insert( convertValue( fld.type(), fld.subType(), res.PQgetvalue( i, 0 ) ) );
     }
   }
   catch ( PGFieldNotFound )
   {
   }
+  return uniqueValues;
 }
 
 QStringList QgsPostgresProvider::uniqueStringsMatching( int index, const QString &substring, int limit, QgsFeedback *feedback ) const

src/providers/postgres/qgspostgresprovider.h

@@ -126,7 +126,7 @@ class QgsPostgresProvider : public QgsVectorDataProvider
     QString dataComment() const override;
     QVariant minimumValue( int index ) const override;
     QVariant maximumValue( int index ) const override;
-    virtual void uniqueValues( int index, QList<QVariant> &uniqueValues, int limit = -1 ) const override;
+    virtual QSet< QVariant > uniqueValues( int index, int limit = -1 ) const override;
     virtual QStringList uniqueStringsMatching( int index, const QString &substring, int limit = -1,
         QgsFeedback *feedback = nullptr ) const override;
     virtual void enumValues( int index, QStringList &enumList ) const override;

src/providers/spatialite/qgsspatialiteprovider.cpp

@@ -3641,17 +3641,17 @@ QVariant QgsSpatiaLiteProvider::maximumValue( int index ) const
 }
 
 // Returns the list of unique values of an attribute
-void QgsSpatiaLiteProvider::uniqueValues( int index, QList < QVariant > &uniqueValues, int limit ) const
+QSet<QVariant> QgsSpatiaLiteProvider::uniqueValues( int index, int limit ) const
 {
   sqlite3_stmt *stmt = nullptr;
   QString sql;
 
-  uniqueValues.clear();
+  QSet<QVariant> uniqueValues;
 
   // get the field name
   if ( index < 0 || index >= mAttributeFields.count() )
   {
-    return; //invalid field
+    return uniqueValues; //invalid field
   }
   QgsField fld = mAttributeFields.at( index );
 
@@ -3674,7 +3674,7 @@ void QgsSpatiaLiteProvider::uniqueValues( int index, QList < QVariant > &uniqueV
   {
     // some error occurred
     QgsMessageLog::logMessage( tr( "SQLite error: %2\nSQL: %1" ).arg( sql, sqlite3_errmsg( mSqliteHandle ) ), tr( "SpatiaLite" ) );
-    return;
+    return uniqueValues;
   }
 
   while ( 1 )
@@ -3694,16 +3694,16 @@ void QgsSpatiaLiteProvider::uniqueValues( int index, QList < QVariant > &uniqueV
       switch ( sqlite3_column_type( stmt, 0 ) )
       {
         case SQLITE_INTEGER:
-          uniqueValues.append( QVariant( sqlite3_column_int( stmt, 0 ) ) );
+          uniqueValues.insert( QVariant( sqlite3_column_int( stmt, 0 ) ) );
           break;
         case SQLITE_FLOAT:
-          uniqueValues.append( QVariant( sqlite3_column_double( stmt, 0 ) ) );
+          uniqueValues.insert( QVariant( sqlite3_column_double( stmt, 0 ) ) );
           break;
         case SQLITE_TEXT:
-          uniqueValues.append( QVariant( QString::fromUtf8( ( const char * ) sqlite3_column_text( stmt, 0 ) ) ) );
+          uniqueValues.insert( QVariant( QString::fromUtf8( ( const char * ) sqlite3_column_text( stmt, 0 ) ) ) );
           break;
         default:
-          uniqueValues.append( QVariant( mAttributeFields.at( index ).type() ) );
+          uniqueValues.insert( QVariant( mAttributeFields.at( index ).type() ) );
           break;
       }
     }
@@ -3711,13 +3711,13 @@ void QgsSpatiaLiteProvider::uniqueValues( int index, QList < QVariant > &uniqueV
     {
       QgsMessageLog::logMessage( tr( "SQLite error: %2\nSQL: %1" ).arg( sql, sqlite3_errmsg( mSqliteHandle ) ), tr( "SpatiaLite" ) );
       sqlite3_finalize( stmt );
-      return;
+      return uniqueValues;
     }
   }
 
   sqlite3_finalize( stmt );
 
-  return;
+  return uniqueValues;
 }
 
 QStringList QgsSpatiaLiteProvider::uniqueStringsMatching( int index, const QString &substring, int limit, QgsFeedback *feedback ) const

src/providers/spatialite/qgsspatialiteprovider.h

@@ -96,7 +96,7 @@ class QgsSpatiaLiteProvider: public QgsVectorDataProvider
     QgsFields fields() const override;
     QVariant minimumValue( int index ) const override;
     QVariant maximumValue( int index ) const override;
-    virtual void uniqueValues( int index, QList < QVariant > &uniqueValues, int limit = -1 ) const override;
+    virtual QSet<QVariant> uniqueValues( int index, int limit = -1 ) const override;
     virtual QStringList uniqueStringsMatching( int index, const QString &substring, int limit = -1,
         QgsFeedback *feedback = nullptr ) const override;
 

tests/src/core/testqgsvectorlayer.cpp

@@ -310,9 +310,8 @@ void TestQgsVectorLayer::uniqueValues()
   QgsVectorLayer *vLayer = static_cast< QgsVectorLayer * >( mpPointsLayer );
 
   //test with invalid field
-  QList<QVariant> values;
-  vLayer->uniqueValues( 1000, values );
-  QCOMPARE( values.length(), 0 );
+  QSet<QVariant> values = vLayer->uniqueValues( 1000 );
+  QCOMPARE( values.count(), 0 );
 }
 
 void TestQgsVectorLayer::minimumValue()

tests/src/python/CMakeLists.txt

@@ -51,6 +51,7 @@ ADD_PYTHON_TEST(PyQgsExpressionLineEdit test_qgsexpressionlineedit.py)
 ADD_PYTHON_TEST(PyQgsExtentGroupBox test_qgsextentgroupbox.py)
 ADD_PYTHON_TEST(PyQgsFeature test_qgsfeature.py)
 ADD_PYTHON_TEST(PyQgsFeatureSink test_qgsfeaturesink.py)
+ADD_PYTHON_TEST(PyQgsFeatureSource test_qgsfeaturesource.py)
 ADD_PYTHON_TEST(PyQgsFieldFormattersTest test_qgsfieldformatters.py)
 ADD_PYTHON_TEST(PyQgsFillSymbolLayers test_qgsfillsymbollayers.py)
 ADD_PYTHON_TEST(PyQgsProject test_qgsproject.py)

tests/src/python/test_qgsfeaturesource.py

@@ -0,0 +1,67 @@
+# -*- coding: utf-8 -*-
+"""QGIS Unit tests for QgsFeatureSource.
+
+.. note:: 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.
+"""
+__author__ = '(C) 2017 by Nyall Dawson'
+__date__ = '26/04/2017'
+__copyright__ = 'Copyright 2017, The QGIS Project'
+# This will get replaced with a git SHA1 when you do a git archive
+__revision__ = '$Format:%H$'
+import qgis  # NOQA
+
+import os
+
+from qgis.core import (QgsVectorLayer,
+                       QgsFeature,
+                       QgsGeometry,
+                       QgsPointXY)
+from qgis.PyQt.QtCore import QVariant
+from qgis.testing import start_app, unittest
+start_app()
+
+
+def createLayerWithFivePoints():
+    layer = QgsVectorLayer("Point?field=fldtxt:string&field=fldint:integer",
+                           "addfeat", "memory")
+    pr = layer.dataProvider()
+    f = QgsFeature()
+    f.setAttributes(["test", 1])
+    f.setGeometry(QgsGeometry.fromPoint(QgsPointXY(100, 200)))
+    f2 = QgsFeature()
+    f2.setAttributes(["test2", 3])
+    f2.setGeometry(QgsGeometry.fromPoint(QgsPointXY(200, 200)))
+    f3 = QgsFeature()
+    f3.setAttributes(["test2", 3])
+    f3.setGeometry(QgsGeometry.fromPoint(QgsPointXY(300, 200)))
+    f4 = QgsFeature()
+    f4.setAttributes(["test3", 3])
+    f4.setGeometry(QgsGeometry.fromPoint(QgsPointXY(400, 300)))
+    f5 = QgsFeature()
+    f5.setAttributes(["test4", 4])
+    f5.setGeometry(QgsGeometry.fromPoint(QgsPointXY(0, 0)))
+    assert pr.addFeatures([f, f2, f3, f4, f5])
+    assert layer.featureCount() == 5
+    return layer
+
+
+class TestQgsFeatureSource(unittest.TestCase):
+
+    def testUniqueValues(self):
+        """
+        Test retrieving unique values using base class method
+        """
+
+        # memory provider uses base class method
+        layer = createLayerWithFivePoints()
+        self.assertFalse(layer.dataProvider().uniqueValues(-1))
+        self.assertFalse(layer.dataProvider().uniqueValues(100))
+        self.assertEqual(layer.dataProvider().uniqueValues(0), {'test', 'test2', 'test3', 'test4'})
+        self.assertEqual(layer.dataProvider().uniqueValues(1), {1, 3, 3, 4})
+
+
+if __name__ == '__main__':
+    unittest.main()