[forms][feature] Value relation: more options for sorting (#59404)

Implements a few newsorting options for the value relation widget:

- reverse order
- order by a specific field

the default behavior is unchanged (Key).

Fixes #54133

Funded by: Consorzio della Bonifica Renana

src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp

@@ -31,16 +31,6 @@ using namespace nlohmann;
 
 #include <QSettings>
 
-bool orderByKeyLessThan( const QgsValueRelationFieldFormatter::ValueRelationItem &p1, const QgsValueRelationFieldFormatter::ValueRelationItem &p2 )
-{
-  return p1.group == p2.group ? qgsVariantLessThan( p1.key, p2.key ) : qgsVariantLessThan( p1.group, p2.group );
-}
-
-bool orderByValueLessThan( const QgsValueRelationFieldFormatter::ValueRelationItem &p1, const QgsValueRelationFieldFormatter::ValueRelationItem &p2 )
-{
-  return p1.group == p2.group ? qgsVariantLessThan( p1.value, p2.value ) : qgsVariantLessThan( p1.group, p2.group );
-}
-
 QgsValueRelationFieldFormatter::QgsValueRelationFieldFormatter()
 {
   setFlags( flags() | QgsFieldFormatter::CanProvideAvailableValues );
@@ -176,6 +166,11 @@ QgsValueRelationFieldFormatter::ValueRelationCache QgsValueRelationFieldFormatte
   }
 
   QgsFeatureIterator fit = layer->getFeatures( request );
+  const bool orderByField { config.value( QStringLiteral( "OrderByField" ) ).toBool() };
+  const int fieldIdx { orderByField ? layer->fields().lookupField( config.value( QStringLiteral( "OrderByFieldName" ) ).toString() ) : -1 };
+  const bool reverseSort { config.value( QStringLiteral( "OrderByDescending" ) ).toBool() };
+
+  QMap<QVariant, QVariant> orderByFieldValues;
 
   QgsFeature f;
   while ( fit.nextFeature( f ) )
@@ -187,16 +182,47 @@ QgsValueRelationFieldFormatter::ValueRelationCache QgsValueRelationFieldFormatte
       description = descriptionExpression.evaluate( &context ).toString();
     }
     const QVariant group = groupIdx > -1 ? f.attribute( groupIdx ) : QVariant();
-    cache.append( ValueRelationItem( f.attribute( keyIdx ), f.attribute( valueIdx ).toString(), description, group ) );
+    const QVariant keyValue = f.attribute( keyIdx );
+    if ( fieldIdx != -1 )
+    {
+      orderByFieldValues.insert( keyValue, f.attribute( fieldIdx ) );
+    }
+    cache.append( ValueRelationItem( keyValue, f.attribute( valueIdx ).toString(), description, group ) );
   }
 
+
   if ( config.value( QStringLiteral( "OrderByValue" ) ).toBool() )
   {
-    std::sort( cache.begin(), cache.end(), orderByValueLessThan );
+    std::sort( cache.begin(), cache.end(), [&reverseSort]( const QgsValueRelationFieldFormatter::ValueRelationItem & p1, const QgsValueRelationFieldFormatter::ValueRelationItem & p2 ) -> bool
+    {
+      if ( reverseSort )
+        return p1.group == p2.group ? qgsVariantGreaterThan( p1.value, p2.value ) : qgsVariantGreaterThan( p1.group, p2.group );
+      else
+        return p1.group == p2.group ? qgsVariantLessThan( p1.value, p2.value ) : qgsVariantLessThan( p1.group, p2.group );
+    } );
   }
+  // Order by field
+  else if ( fieldIdx != -1 )
+  {
+    std::sort( cache.begin(), cache.end(), [&reverseSort, &orderByFieldValues]( const QgsValueRelationFieldFormatter::ValueRelationItem & p1, const QgsValueRelationFieldFormatter::ValueRelationItem & p2 ) -> bool
+    {
+      if ( reverseSort )
+        return p1.group == p2.group ? qgsVariantGreaterThan( orderByFieldValues.value( p1.key ), orderByFieldValues.value( p2.key ) ) : qgsVariantGreaterThan( p1.group, p2.group );
+      else
+        return p1.group == p2.group ? qgsVariantLessThan( orderByFieldValues.value( p1.key ), orderByFieldValues.value( p2.key ) ) : qgsVariantLessThan( p1.group, p2.group );
+
+    } );
+  }
+  // OrderByKey is the default
   else
   {
-    std::sort( cache.begin(), cache.end(), orderByKeyLessThan );
+    std::sort( cache.begin(), cache.end(), [&reverseSort]( const QgsValueRelationFieldFormatter::ValueRelationItem & p1, const QgsValueRelationFieldFormatter::ValueRelationItem & p2 ) -> bool
+    {
+      if ( reverseSort )
+        return p1.group == p2.group ? qgsVariantGreaterThan( p1.key, p2.key ) : qgsVariantGreaterThan( p1.group, p2.group );
+      else
+        return p1.group == p2.group ? qgsVariantLessThan( p1.key, p2.key ) : qgsVariantLessThan( p1.group, p2.group );
+    } );
   }
 
   return cache;

src/gui/editorwidgets/qgsvaluerelationconfigdlg.cpp

@@ -31,12 +31,20 @@ QgsValueRelationConfigDlg::QgsValueRelationConfigDlg( QgsVectorLayer *vl, int fi
   mGroupColumn->setLayer( mLayerName->currentLayer() );
   mGroupColumn->setAllowEmptyFieldName( true );
   mDescriptionExpression->setLayer( mLayerName->currentLayer() );
+  mOrderByFieldName->setLayer( mLayerName->currentLayer() );
+  mOrderByFieldName->setAllowEmptyFieldName( false );
   connect( mLayerName, &QgsMapLayerComboBox::layerChanged, mKeyColumn, &QgsFieldComboBox::setLayer );
   connect( mLayerName, &QgsMapLayerComboBox::layerChanged, mValueColumn, &QgsFieldComboBox::setLayer );
   connect( mLayerName, &QgsMapLayerComboBox::layerChanged, mGroupColumn, &QgsFieldComboBox::setLayer );
   connect( mLayerName, &QgsMapLayerComboBox::layerChanged, mDescriptionExpression, &QgsFieldExpressionWidget::setLayer );
   connect( mLayerName, &QgsMapLayerComboBox::layerChanged, this, &QgsValueRelationConfigDlg::layerChanged );
   connect( mEditExpression, &QAbstractButton::clicked, this, &QgsValueRelationConfigDlg::editExpression );
+  connect( mOrderByField, &QAbstractButton::toggled, mOrderByFieldName, [ = ]( bool enabled )
+  {
+    mOrderByFieldName->setEnabled( enabled );
+  } );
+
+  mOrderByGroupBox->setCollapsed( true );
 
   mNofColumns->setMinimum( 1 );
   mNofColumns->setMaximum( 10 );
@@ -93,6 +101,10 @@ QVariantMap QgsValueRelationConfigDlg::config()
   cfg.insert( QStringLiteral( "NofColumns" ), mNofColumns->value() );
   cfg.insert( QStringLiteral( "AllowNull" ), mAllowNull->isChecked() );
   cfg.insert( QStringLiteral( "OrderByValue" ), mOrderByValue->isChecked() );
+  cfg.insert( QStringLiteral( "OrderByKey" ), mOrderByKey->isChecked() );
+  cfg.insert( QStringLiteral( "OrderByField" ), mOrderByField->isChecked() );
+  cfg.insert( QStringLiteral( "OrderByFieldName" ), mOrderByFieldName->currentField() );
+  cfg.insert( QStringLiteral( "OrderByDescending" ), mOrderByDescending->isChecked() );
   cfg.insert( QStringLiteral( "FilterExpression" ), mFilterExpression->toPlainText() );
   cfg.insert( QStringLiteral( "UseCompleter" ), mUseCompleter->isChecked() );
   const Qt::MatchFlags completerMatchFlags { mCompleterMatchFromStart->isChecked() ? Qt::MatchFlag::MatchStartsWith : Qt::MatchFlag::MatchContains };
@@ -105,6 +117,7 @@ void QgsValueRelationConfigDlg::setConfig( const QVariantMap &config )
 {
   QgsVectorLayer *lyr = QgsValueRelationFieldFormatter::resolveLayer( config, QgsProject::instance() );
   mLayerName->setLayer( lyr );
+  mOrderByFieldName->setLayer( lyr );
   mKeyColumn->setField( config.value( QStringLiteral( "Key" ) ).toString() );
   mValueColumn->setField( config.value( QStringLiteral( "Value" ) ).toString() );
   mGroupColumn->setField( config.value( QStringLiteral( "Group" ) ).toString() );
@@ -119,6 +132,22 @@ void QgsValueRelationConfigDlg::setConfig( const QVariantMap &config )
   }
   mAllowNull->setChecked( config.value( QStringLiteral( "AllowNull" ) ).toBool() );
   mOrderByValue->setChecked( config.value( QStringLiteral( "OrderByValue" ) ).toBool() );
+  mOrderByField->setChecked( config.value( QStringLiteral( "OrderByField" ) ).toBool() );
+  mOrderByKey->setChecked( config.value( QStringLiteral( "OrderByKey" ) ).toBool() );
+  mOrderByFieldName->setField( config.value( QStringLiteral( "OrderByFieldName" ) ).toString() );
+  mOrderByDescending->setChecked( config.value( QStringLiteral( "OrderByDescending" ) ).toBool() );
+
+  if ( !mOrderByField->isChecked() && !mOrderByValue->isChecked() && !mOrderByKey->isChecked() )
+  {
+    mOrderByKey->setChecked( true );
+  }
+
+  // order by key is the default, if it is not checked, expand the config
+  if ( !mOrderByKey->isChecked() )
+  {
+    mOrderByGroupBox->setCollapsed( false );
+  }
+
   mFilterExpression->setPlainText( config.value( QStringLiteral( "FilterExpression" ) ).toString() );
   mUseCompleter->setChecked( config.value( QStringLiteral( "UseCompleter" ) ).toBool() );
   // Default is MatchStartsWith for backwards compatibility
@@ -130,6 +159,7 @@ void QgsValueRelationConfigDlg::layerChanged()
 {
   mFilterExpression->setEnabled( qobject_cast<QgsVectorLayer *>( mLayerName->currentLayer() ) );
   mEditExpression->setEnabled( qobject_cast<QgsVectorLayer *>( mLayerName->currentLayer() ) );
+  mOrderByFieldName->setLayer( mLayerName->currentLayer() );
 }
 
 void QgsValueRelationConfigDlg::editExpression()

src/ui/editorwidgets/qgsvaluerelationconfigdlgbase.ui

@@ -6,15 +6,116 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>318</width>
+    <width>342</width>
-    <height>490</height>
+    <height>620</height>
    </rect>
   </property>
   <property name="windowTitle">
    <string notr="true">Form</string>
   </property>
   <layout class="QGridLayout" name="gridLayout" columnstretch="0,0">
-   <item row="14" column="0" colspan="2">
+   <item row="2" column="0">
+    <widget class="QLabel" name="label_6">
+     <property name="text">
+      <string>Key column</string>
+     </property>
+     <property name="buddy">
+      <cstring>mKeyColumn</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="14" column="0">
+    <widget class="QCheckBox" name="mUseCompleter">
+     <property name="text">
+      <string>Use completer</string>
+     </property>
+    </widget>
+   </item>
+   <item row="10" column="0">
+    <widget class="QLabel" name="label">
+     <property name="text">
+      <string>Description</string>
+     </property>
+    </widget>
+   </item>
+   <item row="16" column="1">
+    <widget class="QgsSpinBox" name="mNofColumns">
+     <property name="sizePolicy">
+      <sizepolicy hsizetype="Expanding" vsizetype="Preferred">
+       <horstretch>1</horstretch>
+       <verstretch>0</verstretch>
+      </sizepolicy>
+     </property>
+    </widget>
+   </item>
+   <item row="8" column="0">
+    <widget class="QLabel" name="label_9">
+     <property name="text">
+      <string>Group column</string>
+     </property>
+     <property name="buddy">
+      <cstring>mGroupColumn</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="20" column="0" colspan="2">
+    <widget class="QTextEdit" name="mFilterExpression"/>
+   </item>
+   <item row="1" column="1">
+    <widget class="QgsMapLayerComboBox" name="mLayerName"/>
+   </item>
+   <item row="2" column="1">
+    <widget class="QgsFieldComboBox" name="mKeyColumn"/>
+   </item>
+   <item row="0" column="0" colspan="2">
+    <widget class="QLabel" name="label_8">
+     <property name="text">
+      <string>Select layer, key column and value column</string>
+     </property>
+    </widget>
+   </item>
+   <item row="15" column="0" colspan="2">
+    <widget class="QCheckBox" name="mAllowMulti">
+     <property name="text">
+      <string>Allow multiple selections</string>
+     </property>
+    </widget>
+   </item>
+   <item row="1" column="0">
+    <widget class="QLabel" name="label_5">
+     <property name="text">
+      <string>Layer</string>
+     </property>
+     <property name="buddy">
+      <cstring>mLayerName</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="11" column="0" colspan="2">
+    <widget class="QCheckBox" name="mAllowNull">
+     <property name="text">
+      <string>Allow NULL value</string>
+     </property>
+    </widget>
+   </item>
+   <item row="3" column="0">
+    <widget class="QLabel" name="label_7">
+     <property name="text">
+      <string>Value column</string>
+     </property>
+     <property name="buddy">
+      <cstring>mValueColumn</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="14" column="1">
+    <widget class="QCheckBox" name="mCompleterMatchFromStart">
+     <property name="text">
+      <string>Only match from the beginning of the string</string>
+     </property>
+    </widget>
+   </item>
+   <item row="17" column="0" colspan="2">
     <layout class="QHBoxLayout" name="horizontalLayout">
      <item>
       <widget class="QLabel" name="label_19">
@@ -32,7 +133,7 @@
         <enum>Qt::RightToLeft</enum>
        </property>
        <property name="icon">
-        <iconset>
+        <iconset resource="../../../images/images.qrc">
          <normaloff>:/images/themes/default/mIconExpression.svg</normaloff>:/images/themes/default/mIconExpression.svg</iconset>
        </property>
       </widget>
@@ -52,137 +153,85 @@
      </item>
     </layout>
    </item>
-   <item row="13" column="0">
+   <item row="8" column="1">
-    <widget class="QLabel" name="label_nofColumns">
-     <property name="text">
-      <string>Number of columns</string>
-     </property>
-    </widget>
-   </item>
-   <item row="17" column="0" colspan="2">
-    <widget class="QTextEdit" name="mFilterExpression"/>
-   </item>
-   <item row="0" column="0" colspan="2">
-    <widget class="QLabel" name="label_8">
-     <property name="text">
-      <string>Select layer, key column and value column</string>
-     </property>
-    </widget>
-   </item>
-   <item row="1" column="0">
-    <widget class="QLabel" name="label_5">
-     <property name="text">
-      <string>Layer</string>
-     </property>
-     <property name="buddy">
-      <cstring>mLayerName</cstring>
-     </property>
-    </widget>
-   </item>
-   <item row="3" column="1">
-    <widget class="QgsFieldComboBox" name="mValueColumn"/>
-   </item>
-   <item row="4" column="0" colspan="2">
-    <widget class="QCheckBox" name="mOrderByValue">
-     <property name="text">
-      <string>Order by value</string>
-     </property>
-    </widget>
-   </item>
-   <item row="1" column="1">
-    <widget class="QgsMapLayerComboBox" name="mLayerName"/>
-   </item>
-   <item row="12" column="0" colspan="2">
-    <widget class="QCheckBox" name="mAllowMulti">
-     <property name="text">
-      <string>Allow multiple selections</string>
-     </property>
-    </widget>
-   </item>
-   <item row="8" column="0" colspan="2">
-    <widget class="QCheckBox" name="mAllowNull">
-     <property name="text">
-      <string>Allow NULL value</string>
-     </property>
-    </widget>
-   </item>
-   <item row="11" column="0">
-    <widget class="QCheckBox" name="mUseCompleter">
-     <property name="text">
-      <string>Use completer</string>
-     </property>
-    </widget>
-   </item>
-   <item row="11" column="1">
-    <widget class="QCheckBox" name="mCompleterMatchFromStart">
-     <property name="text">
-      <string>Only match from the beginning of the string</string>
-     </property>
-    </widget>
-   </item>
-   <item row="2" column="0">
-    <widget class="QLabel" name="label_6">
-     <property name="text">
-      <string>Key column</string>
-     </property>
-     <property name="buddy">
-      <cstring>mKeyColumn</cstring>
-     </property>
-    </widget>
-   </item>
-   <item row="13" column="1">
-    <widget class="QgsSpinBox" name="mNofColumns">
-     <property name="sizePolicy">
-      <sizepolicy hsizetype="Expanding" vsizetype="Preferred">
-       <horstretch>1</horstretch>
-       <verstretch>0</verstretch>
-      </sizepolicy>
-     </property>
-    </widget>
-   </item>
-   <item row="2" column="1">
-    <widget class="QgsFieldComboBox" name="mKeyColumn"/>
-   </item>
-   <item row="3" column="0">
-    <widget class="QLabel" name="label_7">
-     <property name="text">
-      <string>Value column</string>
-     </property>
-     <property name="buddy">
-      <cstring>mValueColumn</cstring>
-     </property>
-    </widget>
-   </item>
-   <item row="5" column="0">
-    <widget class="QLabel" name="label_9">
-     <property name="text">
-      <string>Group column</string>
-     </property>
-     <property name="buddy">
-      <cstring>mGroupColumn</cstring>
-     </property>
-    </widget>
-   </item>
-   <item row="5" column="1">
     <widget class="QgsFieldComboBox" name="mGroupColumn"/>
    </item>
-   <item row="6" column="0" colspan="2">
+   <item row="9" column="0" colspan="2">
     <widget class="QCheckBox" name="mDisplayGroupName">
      <property name="text">
       <string>Display group name</string>
      </property>
     </widget>
    </item>
-   <item row="7" column="0">
+   <item row="3" column="1">
-    <widget class="QLabel" name="label">
+    <widget class="QgsFieldComboBox" name="mValueColumn"/>
+   </item>
+   <item row="16" column="0">
+    <widget class="QLabel" name="label_nofColumns">
      <property name="text">
-      <string>Description</string>
+      <string>Number of columns</string>
      </property>
     </widget>
    </item>
-   <item row="7" column="1">
+   <item row="10" column="1">
     <widget class="QgsFieldExpressionWidget" name="mDescriptionExpression" native="true"/>
    </item>
+   <item row="4" column="0" rowspan="2" colspan="2">
+    <widget class="QgsCollapsibleGroupBox" name="mOrderByGroupBox">
+     <property name="title">
+      <string>Order By</string>
+     </property>
+     <layout class="QVBoxLayout" name="verticalLayout">
+      <item>
+       <widget class="QRadioButton" name="mOrderByKey">
+        <property name="toolTip">
+         <string>Use the values in the key column for sorting</string>
+        </property>
+        <property name="text">
+         <string>Key</string>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <widget class="QRadioButton" name="mOrderByValue">
+        <property name="toolTip">
+         <string>Use the values in the value column for sorting</string>
+        </property>
+        <property name="text">
+         <string>Value</string>
+        </property>
+       </widget>
+      </item>
+      <item>
+       <layout class="QHBoxLayout" name="horizontalLayout_2">
+        <item>
+         <widget class="QRadioButton" name="mOrderByField">
+          <property name="toolTip">
+           <string>Use the values from a specific field for sorting</string>
+          </property>
+          <property name="text">
+           <string>Field</string>
+          </property>
+         </widget>
+        </item>
+        <item>
+         <widget class="QgsFieldComboBox" name="mOrderByFieldName"/>
+        </item>
+       </layout>
+      </item>
+      <item>
+       <widget class="QCheckBox" name="mOrderByDescending">
+        <property name="toolTip">
+         <string>Reverse the sorting</string>
+        </property>
+        <property name="text">
+         <string>Descending order</string>
+        </property>
+       </widget>
+      </item>
+     </layout>
+    </widget>
+   </item>
   </layout>
  </widget>
  <customwidgets>
@@ -207,6 +256,12 @@
    <extends>QComboBox</extends>
    <header>qgsmaplayercombobox.h</header>
   </customwidget>
+  <customwidget>
+   <class>QgsCollapsibleGroupBox</class>
+   <extends>QGroupBox</extends>
+   <header>qgscollapsiblegroupbox.h</header>
+   <container>1</container>
+  </customwidget>
  </customwidgets>
  <tabstops>
   <tabstop>mLayerName</tabstop>
@@ -214,7 +269,6 @@
   <tabstop>mValueColumn</tabstop>
   <tabstop>mGroupColumn</tabstop>
   <tabstop>mDescriptionExpression</tabstop>
-  <tabstop>mOrderByValue</tabstop>
   <tabstop>mAllowNull</tabstop>
   <tabstop>mAllowMulti</tabstop>
   <tabstop>mUseCompleter</tabstop>
@@ -223,6 +277,8 @@
   <tabstop>mEditExpression</tabstop>
   <tabstop>mFilterExpression</tabstop>
  </tabstops>
- <resources/>
+ <resources>
+  <include location="../../../images/images.qrc"/>
+ </resources>
  <connections/>
 </ui>

tests/src/core/testqgsvaluerelationfieldformatter.cpp

@@ -39,6 +39,8 @@ class TestQgsValueRelationFieldFormatter: public QObject
     void testDependencies();
     void testSortValueNull();
     void testGroup();
+    void testOrderBy_data();
+    void testOrderBy();
 
   private:
     std::unique_ptr<QgsVectorLayer> mLayer1;
@@ -112,7 +114,7 @@ void TestQgsValueRelationFieldFormatter::init()
   QgsFeature ft3( mLayer2->fields() );
   ft3.setAttribute( QStringLiteral( "pk" ), 11 );
   ft3.setAttribute( QStringLiteral( "material" ), "iron" );
-  ft3.setAttribute( QStringLiteral( "diameter" ), 120 );
+  ft3.setAttribute( QStringLiteral( "diameter" ), 110 );
   ft3.setAttribute( QStringLiteral( "raccord" ), "sleeve" );
   mLayer2->startEditing();
   mLayer2->addFeature( ft3 );
@@ -121,7 +123,7 @@ void TestQgsValueRelationFieldFormatter::init()
   QgsFeature ft4( mLayer2->fields() );
   ft4.setAttribute( QStringLiteral( "pk" ), 12 );
   ft4.setAttribute( QStringLiteral( "material" ), "steel" );
-  ft4.setAttribute( QStringLiteral( "diameter" ), 120 );
+  ft4.setAttribute( QStringLiteral( "diameter" ), 100 );
   ft4.setAttribute( QStringLiteral( "raccord" ), "collar" );
   mLayer2->startEditing();
   mLayer2->addFeature( ft4 );
@@ -180,5 +182,62 @@ void TestQgsValueRelationFieldFormatter::testGroup()
   QCOMPARE( cache.at( cache.size() - 1 ).group, QVariant( QStringLiteral( "steel" ) ) );
 }
 
+void TestQgsValueRelationFieldFormatter::testOrderBy_data()
+{
+  QTest::addColumn<QString>( "orderBy" );
+  QTest::addColumn<QString>( "fieldName" );
+  QTest::addColumn<QString>( "expectedFirst" );
+  QTest::addColumn<QString>( "expectedLast" );
+
+  QTest::newRow( "orderByDefault(pk)" ) << QString() << QString() << "brides" << "collar";
+  QTest::newRow( "orderByKey(pk)" ) << QString() << QStringLiteral( "Key" ) << "brides" << "collar";
+  QTest::newRow( "orderByValue(raccord)" ) << QString() << QStringLiteral( "Value" ) << "brides" << "collar";
+  QTest::newRow( "orderByField(raccord)" ) << QStringLiteral( "Field" ) << QStringLiteral( "raccord" ) << "brides" << "sleeve";
+  QTest::newRow( "orderByField(diameter)" ) << QStringLiteral( "Field" ) << QStringLiteral( "diameter" ) << "collar" << "brides";
+  QTest::newRow( "orderByField(material)" ) << QStringLiteral( "Field" ) << QStringLiteral( "material" ) << "brides" << "collar";
+}
+
+void TestQgsValueRelationFieldFormatter::testOrderBy()
+{
+
+  QFETCH( QString, orderBy );
+  QFETCH( QString, fieldName );
+  QFETCH( QString, expectedFirst );
+  QFETCH( QString, expectedLast );
+
+  QVariantMap config;
+  config.insert( QStringLiteral( "Layer" ), mLayer2->id() );
+  config.insert( QStringLiteral( "Key" ), QStringLiteral( "pk" ) );
+  config.insert( QStringLiteral( "Value" ), QStringLiteral( "raccord" ) );
+
+  if ( !orderBy.isEmpty() )
+  {
+    config.insert( QStringLiteral( "OrderBy%1" ).arg( orderBy ), true );
+  }
+  if ( !fieldName.isEmpty() )
+  {
+    config.insert( QStringLiteral( "OrderByFieldName" ), fieldName );
+  }
+
+  // Ascending
+  {
+    const QgsValueRelationFieldFormatter formatter;
+    QgsValueRelationFieldFormatter::ValueRelationCache cache = formatter.createCache( config );
+    QVERIFY( !cache.isEmpty() );
+    QCOMPARE( cache.at( 0 ).value, expectedFirst );
+    QCOMPARE( cache.at( mLayer2->featureCount() - 1 ).value, expectedLast );
+  }
+
+  // Descending
+  {
+    config.insert( QStringLiteral( "OrderByDescending" ), true );
+    const QgsValueRelationFieldFormatter formatter;
+    QgsValueRelationFieldFormatter::ValueRelationCache cache = formatter.createCache( config );
+    QVERIFY( !cache.isEmpty() );
+    QCOMPARE( cache.at( 0 ).value, expectedLast );
+    QCOMPARE( cache.at( mLayer2->featureCount() - 1 ).value, expectedFirst );
+  }
+}
+
 QGSTEST_MAIN( TestQgsValueRelationFieldFormatter )
 #include "testqgsvaluerelationfieldformatter.moc"