Add a method which builds an expression to test if a field is equal to a value

pblottiere · pblottiere · commit 15546d84cfbb · 2017-07-05T18:40:08.000+02:00
diff --git a/python/core/expression/qgsexpression.sip b/python/core/expression/qgsexpression.sip
@@ -495,6 +495,17 @@ return index of the function in Functions array
  :rtype: str
 %End
 
+    static QString createFieldEqualityExpression( const QString &fieldName, const QVariant &value );
+%Docstring
+ Create an expression allowing to evaluate if a field is equal to a
+  value. The value may be null.
+ \param fieldName the name of the field
+ \param value the value of the field
+ :return: the expression to evaluate field equality
+.. versionadded:: 3.0
+ :rtype: str
+%End
+
 };
 
 
diff --git a/src/core/expression/qgsexpression.cpp b/src/core/expression/qgsexpression.cpp
@@ -836,6 +836,18 @@ QString QgsExpression::formatPreviewString( const QVariant &value )
   }
 }
 
+QString QgsExpression::createFieldEqualityExpression( const QString &fieldName, const QVariant &value )
+{
+  QString expr;
+
+  if ( value.isNull() )
+    expr = QStringLiteral( "%1 IS NULL" ).arg( quotedColumnRef( fieldName ) );
+  else
+    expr = QStringLiteral( "%1 = %2" ).arg( quotedColumnRef( fieldName ), quotedValue( value ) );
+
+  return expr;
+}
+
 const QgsExpressionNode *QgsExpression::rootNode() const
 {
   return d->mRootNode;
diff --git a/src/core/expression/qgsexpression.h b/src/core/expression/qgsexpression.h
@@ -449,6 +449,15 @@ class CORE_EXPORT QgsExpression
      */
     static QString formatPreviewString( const QVariant &value );
 
+    /** Create an expression allowing to evaluate if a field is equal to a
+     *  value. The value may be null.
+     * \param fieldName the name of the field
+     * \param value the value of the field
+     * \returns the expression to evaluate field equality
+     * \since QGIS 3.0
+     */
+    static QString createFieldEqualityExpression( const QString &fieldName, const QVariant &value );
+
   private:
     void initGeomCalculator();
 
diff --git a/src/core/qgsrelation.cpp b/src/core/qgsrelation.cpp
@@ -170,18 +170,8 @@ QString QgsRelation::getRelatedFeaturesFilter( const QgsFeature &feature ) const
   {
     int referencingIdx = referencingLayer()->fields().indexFromName( fieldPair.referencingField() );
     QgsField referencingField = referencingLayer()->fields().at( referencingIdx );
-    const QString quotedColRef = QgsExpression::quotedColumnRef( fieldPair.referencingField() ) ;
-
     QVariant val( feature.attribute( fieldPair.referencedField() ) );
-
-    if ( val.isNull() )
-    {
-      conditions << QStringLiteral( "%1 IS NULL" ).arg( quotedColRef );
-    }
-    else
-    {
-      conditions << QStringLiteral( "%1 = %2" ).arg( quotedColRef, QgsExpression::quotedValue( val ) );
-    }
+    conditions << QgsExpression::createFieldEqualityExpression( fieldPair.referencingField(), val );
   }
 
   return conditions.join( QStringLiteral( " AND " ) );
diff --git a/src/gui/editorwidgets/qgsrelationreferencewidget.cpp b/src/gui/editorwidgets/qgsrelationreferencewidget.cpp
@@ -861,22 +861,7 @@ void QgsRelationReferenceWidget::filterChanged()
     if ( cb->currentIndex() != 0 )
     {
       const QString fieldName = cb->property( "Field" ).toString();
-
-      if ( cb->currentText() == nullValue.toString() )
-      {
-        filters << QStringLiteral( "\"%1\" IS NULL" ).arg( fieldName );
-      }
-      else
-      {
-        if ( mReferencedLayer->fields().field( fieldName ).type() == QVariant::String )
-        {
-          filters << QStringLiteral( "\"%1\" = '%2'" ).arg( fieldName, cb->currentText() );
-        }
-        else
-        {
-          filters << QStringLiteral( "\"%1\" = %2" ).arg( fieldName, cb->currentText() );
-        }
-      }
+      filters << QgsExpression::createFieldEqualityExpression( fieldName, cb->currentText() );
       attrs << mReferencedLayer->fields().lookupField( fieldName );
     }
   }

Original file line number	Diff line number	Diff line change
`@@ -836,6 +836,18 @@ QString QgsExpression::formatPreviewString( const QVariant &value )`
`836`	`836`	`}`
`837`	`837`	`}`
`838`	`838`
	`839`	`+QString QgsExpression::createFieldEqualityExpression( const QString &fieldName, const QVariant &value )`
	`840`	`+{`
	`841`	`+ QString expr;`
	`842`	`+`
	`843`	`+ if ( value.isNull() )`
	`844`	`+ expr = QStringLiteral( "%1 IS NULL" ).arg( quotedColumnRef( fieldName ) );`
	`845`	`+ else`
	`846`	`+ expr = QStringLiteral( "%1 = %2" ).arg( quotedColumnRef( fieldName ), quotedValue( value ) );`
	`847`	`+`
	`848`	`+ return expr;`
	`849`	`+}`
	`850`	`+`
`839`	`851`	`const QgsExpressionNode *QgsExpression::rootNode() const`
`840`	`852`	`{`
`841`	`853`	`return d->mRootNode;`