From 3bcfda6b18e6bc82cdbd9e5144e9a41300f16a60 Mon Sep 17 00:00:00 2001
From: Mathieu Pellerin <nirvn.asia@gmail.com>
Date: Mon, 12 Aug 2024 10:37:11 +0700
Subject: [PATCH] Harmonize handling of QField's (multi)value relation editor
 widget with that of QGIS

---
 src/core/featurechecklistmodel.cpp      | 25 +++++++++++++------------
 src/qml/editorwidgets/ValueRelation.qml |  2 +-
 2 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/src/core/featurechecklistmodel.cpp b/src/core/featurechecklistmodel.cpp
index f26c0c6878..09a799336b 100644
--- a/src/core/featurechecklistmodel.cpp
+++ b/src/core/featurechecklistmodel.cpp
@@ -61,8 +61,6 @@ QHash<int, QByteArray> FeatureCheckListModel::roleNames() const
 
 QVariant FeatureCheckListModel::attributeValue() const
 {
-  QVariant value;
-
   QVariantList vl;
   //store as QVariantList because the field type supports data structure
   for ( const QString &s : std::as_const( mCheckedEntries ) )
@@ -83,23 +81,26 @@ QVariant FeatureCheckListModel::attributeValue() const
     }
   }
 
-  if ( mAllowMulti )
+  QVariant value;
+  if ( !vl.isEmpty() )
   {
-    if ( mAttributeField.type() == QMetaType::QVariantMap || mAttributeField.type() == QMetaType::QVariantList || mAttributeField.type() == QMetaType::QStringList )
+    if ( mAllowMulti )
     {
-      value = vl;
+      if ( mAttributeField.type() == QMetaType::QVariantMap || mAttributeField.type() == QMetaType::QVariantList || mAttributeField.type() == QMetaType::QStringList )
+      {
+        value = vl;
+      }
+      else
+      {
+        //make string
+        value = QgsPostgresStringUtils::buildArray( vl );
+      }
     }
     else
     {
-      //make string
-      value = QgsPostgresStringUtils::buildArray( vl );
+      value = vl.first();
     }
   }
-  else
-  {
-    value = vl.first();
-  }
-
   return value;
 }
 
diff --git a/src/qml/editorwidgets/ValueRelation.qml b/src/qml/editorwidgets/ValueRelation.qml
index 920dad58dc..c5deaf22cc 100644
--- a/src/qml/editorwidgets/ValueRelation.qml
+++ b/src/qml/editorwidgets/ValueRelation.qml
@@ -42,7 +42,7 @@ EditorWidgetBase {
     attributeValue: value !== undefined ? value : ""
 
     onListUpdated: {
-      valueChangeRequested(attributeValue, false);
+      valueChangeRequested(attributeValue, attributeValue === "");
     }
   }