Merge pull request #6615 from elpaso/bugfix-16967-multi-in-value-relation

[bugfix] value relation widget with Allow multiple selection doesn't resolve

python/core/fieldformatter/qgsvaluerelationfieldformatter.sip.in

@@ -63,6 +63,17 @@ This can be used to keep the value map in the local memory
 if doing multiple lookups in a loop.
 
 .. versionadded:: 3.0
+%End
+
+    static QStringList valueToStringList( const QVariant &value );
+%Docstring
+Utility to convert an array or a string representation of and array ``value`` to a string list
+
+:param value: The value to be converted
+
+:return: A string list
+
+.. versionadded:: 3.2
 %End
 };
 

src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp

@@ -54,7 +54,7 @@ QString QgsValueRelationFieldFormatter::representValue( QgsVectorLayer *layer, i
 
   if ( config.value( QStringLiteral( "AllowMulti" ) ).toBool() )
   {
-    QStringList keyList = value.toString().remove( QChar( '{' ) ).remove( QChar( '}' ) ).split( ',' );
+    QStringList keyList = valueToStringList( value );
     QStringList valueList;
 
     for ( const QgsValueRelationFieldFormatter::ValueRelationItem &item : qgis::as_const( vrCache ) )
@@ -142,3 +142,23 @@ QgsValueRelationFieldFormatter::ValueRelationCache QgsValueRelationFieldFormatte
 
   return cache;
 }
+
+QStringList QgsValueRelationFieldFormatter::valueToStringList( const QVariant &value )
+{
+  QStringList checkList;
+  if ( value.type() == QVariant::StringList )
+    checkList = value.toStringList();
+  else if ( value.type() == QVariant::String )
+    checkList = value.toString().remove( QChar( '{' ) ).remove( QChar( '}' ) ).split( ',' );
+  else if ( value.type() == QVariant::List )
+  {
+    QVariantList valuesList( value.toList( ) );
+    for ( const QVariant &listItem : qgis::as_const( valuesList ) )
+    {
+      QString v( listItem.toString( ) );
+      if ( ! v.isEmpty() )
+        checkList.append( v );
+    }
+  }
+  return checkList;
+}

src/core/fieldformatter/qgsvaluerelationfieldformatter.h

@@ -70,6 +70,15 @@ class CORE_EXPORT QgsValueRelationFieldFormatter : public QgsFieldFormatter
      * \since QGIS 3.0
      */
     static QgsValueRelationFieldFormatter::ValueRelationCache createCache( const QVariantMap &config );
+
+    /**
+     * Utility to convert an array or a string representation of and array \a value to a string list
+     *
+     * \param value The value to be converted
+     * \return A string list
+     * \since QGIS 3.2
+     */
+    static QStringList valueToStringList( const QVariant &value );
 };
 
 Q_DECLARE_METATYPE( QgsValueRelationFieldFormatter::ValueRelationCache )

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.cpp

@@ -151,11 +151,7 @@ void QgsValueRelationWidgetWrapper::setValue( const QVariant &value )
 {
   if ( mListWidget )
   {
-    QStringList checkList;
-    if ( value.type() == QVariant::StringList )
-      checkList = value.toStringList();
-    else if ( value.type() == QVariant::String )
-      checkList = value.toString().remove( QChar( '{' ) ).remove( QChar( '}' ) ).split( ',' );
+    QStringList checkList( QgsValueRelationFieldFormatter::valueToStringList( value ) );
 
     for ( int i = 0; i < mListWidget->count(); ++i )
     {

tests/src/python/test_qgsfieldformatters.py

@@ -107,6 +107,16 @@ class TestQgsValueRelationFieldFormatter(unittest.TestCase):
 
         QgsProject.instance().removeMapLayer(second_layer.id())
 
+    def test_valueToStringList(self):
+
+        def _test(a, b):
+            self.assertEqual(QgsValueRelationFieldFormatter.valueToStringList(a), b)
+
+        _test([1, 2, 3], ["1", "2", "3"])
+        _test("{1,2,3}", ["1", "2", "3"])
+        _test(['1', '2', '3'], ["1", "2", "3"])
+        _test('not an array', ['not an array'])
+
 
 class TestQgsRelationReferenceFieldFormatter(unittest.TestCase):