Fix relation reference widget when 'Chain Filters' is activated. Fixes …

…#16903

src/gui/editorwidgets/qgsrelationreferencewidget.cpp

@@ -814,6 +814,29 @@ void QgsRelationReferenceWidget::filterChanged()
 
   Q_ASSERT( scb );
 
+  QgsFeature f;
+  QgsFeatureIds featureIds;
+  QString filterExpression;
+
+  Q_FOREACH ( QComboBox *cb, mFilterComboBoxes )
+  {
+    if ( cb->currentIndex() != 0 )
+    {
+      const QString fieldName = cb->property( "Field" ).toString();
+
+      if ( cb->currentText() == nullValue.toString() )
+      {
+        filters << QStringLiteral( "\"%1\" IS NULL" ).arg( fieldName );
+      }
+      else
+      {
+        filters << QgsExpression::createFieldEqualityExpression( fieldName, cb->currentText() );
+      }
+      attrs << mReferencedLayer->fields().lookupField( fieldName );
+    }
+  }
+
+  bool filtered = false;
   if ( mChainFilters )
   {
     QComboBox *ccb = nullptr;
@@ -834,6 +857,9 @@ void QgsRelationReferenceWidget::filterChanged()
       }
       else
       {
+        const QString fieldName = cb->property( "Field" ).toString();
+        filtered = true;
+
         cb->blockSignals( true );
         cb->clear();
         cb->addItem( cb->property( "FieldAlias" ).toString() );
@@ -843,8 +869,29 @@ void QgsRelationReferenceWidget::filterChanged()
         QStringList texts;
         Q_FOREACH ( const QString &txt, mFilterCache[ccb->property( "Field" ).toString()][ccb->currentText()] )
         {
-          texts << txt;
+          QStringList filtersAttrs = filters;
+          filtersAttrs << QgsExpression::createFieldEqualityExpression( fieldName, txt );
+          QString expression = filtersAttrs.join( QStringLiteral( " AND " ) );
+
+          QgsAttributeList subset = attrs;
+          subset << mReferencedLayer->fields().lookupField( fieldName );
+
+          QgsFeatureIterator it( mMasterModel->layerCache()->getFeatures( QgsFeatureRequest().setFilterExpression( expression ).setSubsetOfAttributes( subset ) ) );
+
+          bool found = false;
+          while ( it.nextFeature( f ) )
+          {
+            if ( !featureIds.contains( f.id() ) )
+              featureIds << f.id();
+
+            found = true;
+          }
+
+          // item is only provided if at least 1 feature exists
+          if ( found )
+            texts << txt;
         }
+
         texts.sort();
         cb->addItems( texts );
 
@@ -856,34 +903,16 @@ void QgsRelationReferenceWidget::filterChanged()
     }
   }
 
-  Q_FOREACH ( QComboBox *cb, mFilterComboBoxes )
+  if ( !mChainFilters || ( mChainFilters && !filtered ) )
   {
-    if ( cb->currentIndex() != 0 )
-    {
-      const QString fieldName = cb->property( "Field" ).toString();
-
-      if ( cb->currentText() == nullValue.toString() )
-      {
-        filters << QStringLiteral( "\"%1\" IS NULL" ).arg( fieldName );
-      }
-      else
-      {
-        filters << QgsExpression::createFieldEqualityExpression( fieldName, cb->currentText() );
-      }
-      attrs << mReferencedLayer->fields().lookupField( fieldName );
-    }
-  }
-
-  QString filterExpression = filters.join( QStringLiteral( " AND " ) );
+    filterExpression = filters.join( QStringLiteral( " AND " ) );
 
-  QgsFeatureIterator it( mMasterModel->layerCache()->getFeatures( QgsFeatureRequest().setFilterExpression( filterExpression ).setSubsetOfAttributes( attrs ) ) );
+    QgsFeatureIterator it( mMasterModel->layerCache()->getFeatures( QgsFeatureRequest().setFilterExpression( filterExpression ).setSubsetOfAttributes( attrs ) ) );
 
-  QgsFeature f;
-  QgsFeatureIds featureIds;
-
-  while ( it.nextFeature( f ) )
-  {
-    featureIds << f.id();
+    while ( it.nextFeature( f ) )
+    {
+      featureIds << f.id();
+    }
   }
 
   mFilterModel->setFilteredFeatures( featureIds );