[Backport queued_ltr_backports] [ValueRelationWidget] Restore correctly value on widget value changed

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.cpp

@@ -18,16 +18,11 @@
 #include "qgis.h"
 #include "qgsfields.h"
 #include "qgsproject.h"
-#include "qgsvaluerelationwidgetfactory.h"
 #include "qgsvectorlayer.h"
 #include "qgsfilterlineedit.h"
-#include "qgsfeatureiterator.h"
 #include "qgsvaluerelationfieldformatter.h"
 #include "qgsattributeform.h"
-#include "qgsattributes.h"
-#include "qgsjsonutils.h"
 #include "qgspostgresstringutils.h"
-#include "qgsapplication.h"
 
 #include <QComboBox>
 #include <QLineEdit>
@@ -347,6 +342,11 @@ bool QgsValueRelationWidgetWrapper::valid() const
 }
 
 void QgsValueRelationWidgetWrapper::updateValues( const QVariant &value, const QVariantList & )
+{
+  updateValue( value, true );
+}
+
+void QgsValueRelationWidgetWrapper::updateValue( const QVariant &value, bool forceComboInsertion )
 {
   if ( mTableWidget )
   {
@@ -382,7 +382,7 @@ void QgsValueRelationWidgetWrapper::updateValues( const QVariant &value, const Q
     if ( idx == -1 )
     {
       // if value doesn't exist, we show it in '(...)' (just like value map widget)
-      if ( QgsVariantUtils::isNull( value ) )
+      if ( QgsVariantUtils::isNull( value ) || !forceComboInsertion )
       {
         mComboBox->setCurrentIndex( -1 );
       }
@@ -435,7 +435,7 @@ void QgsValueRelationWidgetWrapper::widgetValueChanged( const QString &attribute
     {
       populate();
       // Restore value
-      updateValues( value( ) );
+      updateValue( oldValue, false );
       // If the value has changed as a result of another widget's value change,
       // we need to emit the signal to make sure other dependent widgets are
       // updated.

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.h

@@ -193,6 +193,17 @@ class GUI_EXPORT QgsValueRelationWidgetWrapper : public QgsEditorWidgetWrapper
   private:
     void updateValues( const QVariant &value, const QVariantList & = QVariantList() ) override;
 
+    /**
+     * Set widget wrapper value, called by updateValues()
+     * \param value new value to update the widget with
+     * \param forceComboInsertion if TRUE \a value would be inserted even if it doesn't exist in
+     * combobox items and would appear as '(value)', else value would not be inserted. This has
+     * no effects for widgets other than combobox because other widgets have different behavior:
+     *
+     * - line edit displays '(no selection)' if value doesn't exist
+     * - table widget would check only items existing in value
+     */
+    void updateValue( const QVariant &value, bool forceComboInsertion );
 
     /**
      * Returns the value configured in `NofColumns` or 1 if not

tests/src/gui/testqgsvaluerelationwidgetwrapper.cpp

@@ -1854,7 +1854,9 @@ void TestQgsValueRelationWidgetWrapper::testMultiEditMode()
   cfg.insert( QStringLiteral( "AllowNull" ), false );
   cfg.insert( QStringLiteral( "OrderByValue" ), false );
   cfg.insert( QStringLiteral( "UseCompleter" ), false );
-  cfg.insert( QStringLiteral( "FilterExpression" ), QStringLiteral( "left(\"name\",4)  = current_value('firstname')" ) );
+
+  // we match only the 3 first character so Jhon and Jhon would work both. Useful for later tests
+  cfg.insert( QStringLiteral( "FilterExpression" ), QStringLiteral( "left(\"name\",3)  = left(current_value('firstname'),3)" ) );
 
   people->setEditorWidgetSetup( 1, QgsEditorWidgetSetup( QStringLiteral( "ValueRelation" ), cfg ) );
 
@@ -1891,6 +1893,14 @@ void TestQgsValueRelationWidgetWrapper::testMultiEditMode()
   QCOMPARE( valueRelationWrapper->mComboBox->model()->data( valueRelationWrapper->mComboBox->model()->index( 1, 0 ), Qt::DisplayRole ), QStringLiteral( "Jhon F. Kennedy" ) );
   QCOMPARE( valueRelationWrapper->mComboBox->model()->data( valueRelationWrapper->mComboBox->model()->index( 2, 0 ), Qt::DisplayRole ), QStringLiteral( "Jhon Lennon" ) );
 
+  valueRelationWrapper->setValues( QStringLiteral( "Jhon Lennon" ), QVariantList() );
+  QCOMPARE( valueRelationWrapper->mComboBox->currentIndex(), 2 );
+  QCOMPARE( valueRelationWrapper->mComboBox->currentText(), QStringLiteral( "Jhon Lennon" ) );
+
+  firstNameWrapper->setValues( QStringLiteral( "Jho" ), QVariantList() );
+  QCOMPARE( valueRelationWrapper->mComboBox->currentIndex(), 2 );
+  QCOMPARE( valueRelationWrapper->mComboBox->currentText(), QStringLiteral( "Jhon Lennon" ) );
+
   people->rollBack();
   QgsProject::instance()->removeMapLayer( people.get() );
   QgsProject::instance()->removeMapLayer( famous.get() );