Move methods for returning lists of values from a vector layer field

or expression to QgsVectorLayer. Add unit tests.

Author: nyalldawson

python/core/qgsvectorlayer.sip

@@ -1130,6 +1130,25 @@ class QgsVectorLayer : QgsMapLayer
 
     /**Returns maximum value for an attribute column or invalid variant in case of error */
     QVariant maximumValue( int index );
+    
+    /** Fetches all values from a specified field name or expression.
+     * @param fieldOrExpression field name or an expression string
+     * @param ok will be set to false if field or expression is invalid, otherwise true
+     * @returns list of fetched values
+     * @note added in QGIS 2.9
+     * @see getDoubleValues
+     */
+    QList< QVariant > getValues( const QString &fieldOrExpression, bool &ok );
+    
+    /** Fetches all double values from a specified field name or expression. Null values or
+     * invalid expression results are skipped.
+     * @param fieldOrExpression field name or an expression string evaluating to a double value
+     * @param ok will be set to false if field or expression is invalid, otherwise true
+     * @returns list of fetched values
+     * @note added in QGIS 2.9
+     * @see getValues
+     */
+    QList< double > getDoubleValues( const QString &fieldOrExpression, bool &ok );
 
     /** Set the blending mode used for rendering each feature */
     void setFeatureBlendMode( const QPainter::CompositionMode &blendMode );

python/core/symbology-ng/qgsgraduatedsymbolrendererv2.sip

@@ -155,7 +155,8 @@ class QgsGraduatedSymbolRendererV2 : QgsFeatureRendererV2
     //! Evaluates the data expression and returns the list of values from the layer
     //! @param vlayer  The layer for which to evaluate the expression
     //! @note Added in 2.6
-    QList<double> getDataValues( QgsVectorLayer *vlayer );
+    //! @deprecated use QgsVectorLayer::getDoubleValues instead
+    QList<double> getDataValues( QgsVectorLayer *vlayer ) /Deprecated/;
 
     //! Return the label format used to generate default classification labels
     //! @note Added in 2.6

src/core/qgsvectorlayer.cpp

@@ -3142,6 +3142,67 @@ QVariant QgsVectorLayer::maximumValue( int index )
   return QVariant();
 }
 
+QList<QVariant> QgsVectorLayer::getValues( const QString &fieldOrExpression, bool& ok )
+{
+  QList<QVariant> values;
+
+  QScopedPointer<QgsExpression> expression;
+  int attrNum = fieldNameIndex( fieldOrExpression );
+
+  if ( attrNum == -1 )
+  {
+    // try to use expression
+    expression.reset( new QgsExpression( fieldOrExpression ) );
+    if ( expression->hasParserError() || !expression->prepare( pendingFields() ) )
+    {
+      ok = false;
+      return values;
+    }
+  }
+
+  QgsFeature f;
+  QStringList lst;
+  if ( expression.isNull() )
+    lst.append( fieldOrExpression );
+  else
+    lst = expression->referencedColumns();
+
+  QgsFeatureIterator fit = getFeatures( QgsFeatureRequest()
+                                        .setFlags(( expression && expression->needsGeometry() ) ?
+                                                  QgsFeatureRequest::NoFlags :
+                                                  QgsFeatureRequest::NoGeometry )
+                                        .setSubsetOfAttributes( lst, pendingFields() ) );
+
+  // create list of non-null attribute values
+  while ( fit.nextFeature( f ) )
+  {
+    QVariant v = expression ? expression->evaluate( f ) : f.attribute( attrNum );
+    values << v;
+  }
+  ok = true;
+  return values;
+}
+
+QList<double> QgsVectorLayer::getDoubleValues( const QString &fieldOrExpression, bool& ok )
+{
+  QList<double> values;
+
+  QList<QVariant> variantValues = getValues( fieldOrExpression, ok );
+  if ( !ok )
+    return values;
+
+  bool convertOk;
+  foreach ( QVariant value, variantValues )
+  {
+    double val = value.toDouble( &convertOk );
+    if ( convertOk )
+      values << val;
+  }
+  ok = true;
+  return values;
+}
+
+
 /** Write blend mode for features */
 void QgsVectorLayer::setFeatureBlendMode( const QPainter::CompositionMode &featureBlendMode )
 {

src/core/qgsvectorlayer.h

@@ -1493,6 +1493,25 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer
     /**Returns maximum value for an attribute column or invalid variant in case of error */
     QVariant maximumValue( int index );
 
+    /** Fetches all values from a specified field name or expression.
+     * @param fieldOrExpression field name or an expression string
+     * @param ok will be set to false if field or expression is invalid, otherwise true
+     * @returns list of fetched values
+     * @note added in QGIS 2.9
+     * @see getDoubleValues
+     */
+    QList< QVariant > getValues( const QString &fieldOrExpression, bool &ok );
+
+    /** Fetches all double values from a specified field name or expression. Null values or
+     * invalid expression results are skipped.
+     * @param fieldOrExpression field name or an expression string evaluating to a double value
+     * @param ok will be set to false if field or expression is invalid, otherwise true
+     * @returns list of fetched values
+     * @note added in QGIS 2.9
+     * @see getValues
+     */
+    QList< double > getDoubleValues( const QString &fieldOrExpression, bool &ok );
+
     /** Set the blending mode used for rendering each feature */
     void setFeatureBlendMode( const QPainter::CompositionMode &blendMode );
     /** Returns the current blending mode for features */

src/core/symbology-ng/qgsgraduatedsymbolrendererv2.cpp

@@ -817,40 +817,8 @@ QgsGraduatedSymbolRendererV2* QgsGraduatedSymbolRendererV2::createRenderer(
 
 QList<double> QgsGraduatedSymbolRendererV2::getDataValues( QgsVectorLayer *vlayer )
 {
-  QList<double> values;
-
-  QScopedPointer<QgsExpression> expression;
-  int attrNum = vlayer->fieldNameIndex( mAttrName );
-
-  if ( attrNum == -1 )
-  {
-    // try to use expression
-    expression.reset( new QgsExpression( mAttrName ) );
-    if ( expression->hasParserError() || !expression->prepare( vlayer->pendingFields() ) )
-      return values; // should have a means to report errors
-  }
-
-  QgsFeature f;
-  QStringList lst;
-  if ( expression.isNull() )
-    lst.append( mAttrName );
-  else
-    lst = expression->referencedColumns();
-
-  QgsFeatureIterator fit = vlayer->getFeatures( QgsFeatureRequest()
-                           .setFlags(( expression && expression->needsGeometry() ) ?
-                                     QgsFeatureRequest::NoFlags :
-                                     QgsFeatureRequest::NoGeometry )
-                           .setSubsetOfAttributes( lst, vlayer->pendingFields() ) );
-
-  // create list of non-null attribute values
-  while ( fit.nextFeature( f ) )
-  {
-    QVariant v = expression ? expression->evaluate( f ) : f.attribute( attrNum );
-    if ( !v.isNull() )
-      values.append( v.toDouble() );
-  }
-  return values;
+  bool ok;
+  return vlayer->getDoubleValues( mAttrName, ok );
 }
 
 void QgsGraduatedSymbolRendererV2::updateClasses( QgsVectorLayer *vlayer, Mode mode, int nclasses )
@@ -873,10 +841,11 @@ void QgsGraduatedSymbolRendererV2::updateClasses( QgsVectorLayer *vlayer, Mode m
 
   int attrNum = vlayer->fieldNameIndex( mAttrName );
 
+  bool ok;
   if ( attrNum == -1 )
   {
-    values = getDataValues( vlayer );
-    if ( values.isEmpty() )
+    values = vlayer->getDoubleValues( mAttrName, ok );
+    if ( !ok || values.isEmpty() )
       return;
 
     qSort( values ); // vmora: is wondering if O( n log(n) ) is really necessary here, min and max are O( n )
@@ -906,7 +875,7 @@ void QgsGraduatedSymbolRendererV2::updateClasses( QgsVectorLayer *vlayer, Mode m
     // get values from layer
     if ( !valuesLoaded )
     {
-      values = getDataValues( vlayer );
+      values = vlayer->getDoubleValues( mAttrName, ok );
     }
 
     // calculate the breaks

src/core/symbology-ng/qgsgraduatedsymbolrendererv2.h

@@ -184,10 +184,12 @@ class CORE_EXPORT QgsGraduatedSymbolRendererV2 : public QgsFeatureRendererV2
     //! @param nclasses The number of classes to calculate (approximate for some modes)
     //! @note Added in 2.6
     void updateClasses( QgsVectorLayer *vlayer, Mode mode, int nclasses );
+
     //! Evaluates the data expression and returns the list of values from the layer
     //! @param vlayer  The layer for which to evaluate the expression
     //! @note Added in 2.6
-    QList<double> getDataValues( QgsVectorLayer *vlayer );
+    //! @deprecated use QgsVectorLayer::getDoubleValues instead
+    Q_DECL_DEPRECATED QList<double> getDataValues( QgsVectorLayer *vlayer );
 
     //! Return the label format used to generate default classification labels
     //! @note Added in 2.6

tests/src/core/testqgsvectorlayer.cpp

@@ -194,6 +194,54 @@ class TestQgsVectorLayer : public QObject
       QVERIFY( myCount == 3 );
     }
 
+    void QgsVectorLayerGetValues()
+    {
+      QgsVectorLayer* layer = new QgsVectorLayer( "Point?field=col1:real", "layer", "memory" );
+      QVERIFY( layer->isValid() );
+      QgsFeature f1( layer->dataProvider()->fields(), 1 );
+      f1.setAttribute( "col1", 1 );
+      QgsFeature f2( layer->dataProvider()->fields(), 2 );
+      f2.setAttribute( "col1", 2 );
+      QgsFeature f3( layer->dataProvider()->fields(), 3 );
+      f3.setAttribute( "col1", 3 );
+      QgsFeature f4( layer->dataProvider()->fields(), 4 );
+      f4.setAttribute( "col1", QVariant() );
+      layer->dataProvider()->addFeatures( QgsFeatureList() << f1 << f2 << f3 << f4 );
+
+      bool ok;
+      QList<QVariant> varList = layer->getValues( "col1", ok );
+      QVERIFY( ok );
+      QCOMPARE( varList.length(), 4 );
+      QCOMPARE( varList.at( 0 ), QVariant( 1 ) );
+      QCOMPARE( varList.at( 1 ), QVariant( 2 ) );
+      QCOMPARE( varList.at( 2 ), QVariant( 3 ) );
+      QCOMPARE( varList.at( 3 ), QVariant() );
+
+      QList<double> doubleList = layer->getDoubleValues( "col1", ok );
+      QVERIFY( ok );
+      QCOMPARE( doubleList.length(), 3 );
+      QCOMPARE( doubleList.at( 0 ), 1.0 );
+      QCOMPARE( doubleList.at( 1 ), 2.0 );
+      QCOMPARE( doubleList.at( 2 ), 3.0 );
+
+      QList<QVariant> expVarList = layer->getValues( "tostring(col1) || ' '", ok );
+      QVERIFY( ok );
+      QCOMPARE( expVarList.length(), 4 );
+      QCOMPARE( expVarList.at( 0 ).toString(), QString( "1 " ) );
+      QCOMPARE( expVarList.at( 1 ).toString(), QString( "2 " ) );
+      QCOMPARE( expVarList.at( 2 ).toString(), QString( "3 " ) );
+      QCOMPARE( expVarList.at( 3 ), QVariant() );
+
+      QList<double> expDoubleList = layer->getDoubleValues( "col1 * 2", ok );
+      QVERIFY( ok );
+      QCOMPARE( expDoubleList.length(), 3 );
+      QCOMPARE( expDoubleList.at( 0 ), 2.0 );
+      QCOMPARE( expDoubleList.at( 1 ), 4.0 );
+      QCOMPARE( expDoubleList.at( 2 ), 6.0 );
+
+      delete layer;
+    }
+
     void QgsVectorLayerstorageType() {}
     void QgsVectorLayercapabilitiesString() {}
     void QgsVectorLayerdataComment() {}