[attribute form] Fix initial multi editing state of relation referenc…

…e editor widgets

python/PyQt6/core/auto_generated/qgsfeaturepickermodelbase.sip.in

@@ -213,7 +213,7 @@ The index at which the extra identifier value is available within the model.
 
     void extraValueDoesNotExistChanged();
 %Docstring
-Flag indicating that the extraIdentifierValue does not exist in the data.
+Notification that the model has found a feature tied to the extraIdentifierValue.
 %End
 
     void beginUpdate();

python/PyQt6/gui/auto_generated/qgsfeaturelistcombobox.sip.in

@@ -240,6 +240,13 @@ Determines if a NULL value should be available in the list.
 Emitted when the current feature changes
 
 .. versionadded:: 3.16.5
+%End
+
+    void currentFeatureFoundChanged();
+%Docstring
+Emitted when the feature picker model changes its feature found state
+
+.. versionadded:: 3.38
 %End
 
 };

python/core/auto_generated/qgsfeaturepickermodelbase.sip.in

@@ -213,7 +213,7 @@ The index at which the extra identifier value is available within the model.
 
     void extraValueDoesNotExistChanged();
 %Docstring
-Flag indicating that the extraIdentifierValue does not exist in the data.
+Notification that the model has found a feature tied to the extraIdentifierValue.
 %End
 
     void beginUpdate();

python/gui/auto_generated/qgsfeaturelistcombobox.sip.in

@@ -240,6 +240,13 @@ Determines if a NULL value should be available in the list.
 Emitted when the current feature changes
 
 .. versionadded:: 3.16.5
+%End
+
+    void currentFeatureFoundChanged();
+%Docstring
+Emitted when the feature picker model changes its feature found state
+
+.. versionadded:: 3.38
 %End
 
 };

src/core/qgsfeaturepickermodelbase.cpp

@@ -30,7 +30,6 @@ QgsFeaturePickerModelBase::QgsFeaturePickerModelBase( QObject *parent )
   // The fact that the feature changed is a combination of the 2 signals:
   // If the extra value is set to a feature currently not fetched, it will go through an intermediate step while the extra value does not exist (as it call reloadFeature)
   connect( this, &QgsFeaturePickerModelBase::extraIdentifierValueChanged, this, &QgsFeaturePickerModelBase::currentFeatureChanged );
-  connect( this, &QgsFeaturePickerModelBase::extraValueDoesNotExistChanged, this, &QgsFeaturePickerModelBase::currentFeatureChanged );
 }
 
 

src/core/qgsfeaturepickermodelbase.h

@@ -241,7 +241,7 @@ class CORE_EXPORT QgsFeaturePickerModelBase : public QAbstractItemModel SIP_ABST
     void extraIdentifierValueIndexChanged( int index );
 
     /**
-     * Flag indicating that the extraIdentifierValue does not exist in the data.
+     * Notification that the model has found a feature tied to the extraIdentifierValue.
      */
     void extraValueDoesNotExistChanged();
 

src/gui/editorwidgets/qgsrelationreferencewidget.cpp

@@ -494,6 +494,7 @@ void QgsRelationReferenceWidget::init()
 
     // Only connect after iterating, to have only one iterator on the referenced table at once
     connect( mComboBox, &QgsFeatureListComboBox::currentFeatureChanged, this, &QgsRelationReferenceWidget::comboReferenceChanged );
+    connect( mComboBox, &QgsFeatureListComboBox::currentFeatureFoundChanged, this, &QgsRelationReferenceWidget::comboReferenceFoundChanged );
 
     QApplication::restoreOverrideCursor();
 
@@ -626,6 +627,13 @@ void QgsRelationReferenceWidget::comboReferenceChanged()
   emitForeignKeysChanged( mComboBox->identifierValues() );
 }
 
+void QgsRelationReferenceWidget::comboReferenceFoundChanged()
+{
+  mReferencedLayer->getFeatures( mComboBox->currentFeatureRequest() ).nextFeature( mFeature );
+  highlightFeature( mFeature );
+  updateAttributeEditorFrame( mFeature );
+}
+
 void QgsRelationReferenceWidget::updateAttributeEditorFrame( const QgsFeature &feature )
 {
   mOpenFormButton->setEnabled( feature.isValid() );

src/gui/editorwidgets/qgsrelationreferencewidget.h

@@ -294,6 +294,7 @@ class GUI_EXPORT QgsRelationReferenceWidget : public QWidget
     void highlightActionTriggered( QAction *action );
     void deleteHighlight();
     void comboReferenceChanged();
+    void comboReferenceFoundChanged();
     void featureIdentified( const QgsFeature &feature );
     void setMapTool( QgsMapTool *mapTool );
     void unsetMapTool();

src/gui/qgsfeaturelistcombobox.cpp

@@ -65,6 +65,7 @@ QgsFeatureListComboBox::QgsFeatureListComboBox( QWidget *parent )
   connect( mLineEdit, &QgsFilterLineEdit::cleared, this, &QgsFeatureListComboBox::onFilterLineEditCleared );
 
   connect( mModel, &QgsFeatureFilterModel::currentFeatureChanged, this, &QgsFeatureListComboBox::currentFeatureChanged );
+  connect( mModel, &QgsFeatureFilterModel::extraValueDoesNotExistChanged, this, &QgsFeatureListComboBox::currentFeatureFoundChanged );
 
   setToolTip( tr( "Just start typing what you are looking for." ) );
 }

src/gui/qgsfeaturelistcombobox.h

@@ -251,6 +251,12 @@ class GUI_EXPORT QgsFeatureListComboBox : public QComboBox
      */
     void currentFeatureChanged();
 
+    /**
+     * Emitted when the feature picker model changes its feature found state
+     * \since QGIS 3.38
+     */
+    void currentFeatureFoundChanged();
+
   private slots:
     void onCurrentTextChanged( const QString &text );
     void onFilterLineEditCleared();