Fixes for refinement of rules.

- quoting of columns (#5536 and #5542)
- quoting of string
- do not quote of numbers (avoids type cast during evaluation)
- use at least 4 floating point digits for doubles

python/core/qgsexpression.sip

@@ -122,6 +122,8 @@ public:
 
     //! return quoted column reference (in double quotes)
     static QString quotedColumnRef( QString name );
+    //! return quoted string (in single quotes)
+    static QString quotedString( QString text );
 
     //////
 

src/core/qgsexpression.h

@@ -209,6 +209,8 @@ class CORE_EXPORT QgsExpression
 
     //! return quoted column reference (in double quotes)
     static QString quotedColumnRef( QString name ) { return QString( "\"%1\"" ).arg( name.replace( "\"", "\"\"" ) ); }
+    //! return quoted string (in single quotes)
+    static QString quotedString( QString text ) { return QString( "'%1'" ).arg( text.replace( "'", "''" ) ); }
 
     //////
 

src/core/symbology-ng/qgsrulebasedrendererv2.cpp

@@ -803,7 +803,18 @@ void QgsRuleBasedRendererV2::refineRuleCategories( QgsRuleBasedRendererV2::Rule*
 {
   foreach( const QgsRendererCategoryV2& cat, r->categories() )
   {
-    QString filter = QString( "%1 = '%2'" ).arg( r->classAttribute() ).arg( cat.value().toString() );
+    QString attr = QgsExpression::quotedColumnRef( r->classAttribute() );
+    QString value;
+    // not quoting numbers saves a type cast
+    if ( cat.value().type() == QVariant::Int )
+      value = cat.value().toString();
+    else if ( cat.value().type() == QVariant::Double )
+      // we loose precision here - so we may miss some categories :-(
+      // TODO: have a possibility to construct expressions directly as a parse tree to avoid loss of precision
+      value = QString::number( cat.value().toDouble(), 'f', 4 );
+    else
+      value = QgsExpression::quotedString( cat.value().toString() );
+    QString filter = QString( "%1 = %2" ).arg( attr ).arg( value );
     QString label = filter;
     initialRule->appendChild( new Rule( cat.symbol()->clone(), 0, 0, filter, label ) );
   }
@@ -813,7 +824,12 @@ void QgsRuleBasedRendererV2::refineRuleRanges( QgsRuleBasedRendererV2::Rule* ini
 {
   foreach( const QgsRendererRangeV2& rng, r->ranges() )
   {
-    QString filter = QString( "%1 >= '%2' AND %1 <= '%3'" ).arg( r->classAttribute() ).arg( rng.lowerValue() ).arg( rng.upperValue() );
+    // due to the loss of precision in double->string conversion we may miss out values at the limit of the range
+    // TODO: have a possibility to construct expressions directly as a parse tree to avoid loss of precision
+    QString attr = QgsExpression::quotedColumnRef( r->classAttribute() );
+    QString filter = QString( "%1 >= %2 AND %1 <= %3" ).arg( attr )
+            .arg( QString::number( rng.lowerValue(), 'f', 4 ) )
+            .arg( QString::number( rng.upperValue(), 'f', 4 ) );
     QString label = filter;
     initialRule->appendChild( new Rule( rng.symbol()->clone(), 0, 0, filter, label ) );
   }

src/gui/symbology-ng/qgsgraduatedsymbolrendererv2widget.cpp

@@ -325,8 +325,8 @@ void QgsGraduatedSymbolRendererV2Widget::changeRange( int rangeIdx )
   QgsLUDialog dialog( this );
 
   const QgsRendererRangeV2& range = mRenderer->ranges()[rangeIdx];
-  dialog.setLowerValue( QString( "%1" ).arg( range.lowerValue() ) );
-  dialog.setUpperValue( QString( "%1" ).arg( range.upperValue() ) );
+  dialog.setLowerValue( QString::number( range.lowerValue(), 'f', 4 ) );
+  dialog.setUpperValue( QString::number( range.upperValue(), 'f', 4 ) );
 
   if ( dialog.exec() == QDialog::Accepted )
   {