Allow setting merge policy in the GUI

src/gui/attributeformconfig/qgsattributetypedialog.cpp

@@ -126,6 +126,29 @@ QgsAttributeTypeDialog::QgsAttributeTypeDialog( QgsVectorLayer *vl, int fieldIdx
   mDuplicatePolicyComboBox->addItem( tr( "Remove Value" ), QVariant::fromValue( Qgis::FieldDuplicatePolicy::UnsetField ) );
   connect( mDuplicatePolicyComboBox, qOverload<int>( &QComboBox::currentIndexChanged ), this, &QgsAttributeTypeDialog::updateDuplicatePolicyLabel );
   updateDuplicatePolicyLabel();
+
+  if ( mLayer->isSpatial() )
+  {
+    mMergePolicyComboBox->addItem( tr( "Remove Value" ), QVariant::fromValue( Qgis::FieldDomainMergePolicy::UnsetField ) );
+    mMergePolicyComboBox->addItem( tr( "Use Default Value" ), QVariant::fromValue( Qgis::FieldDomainMergePolicy::DefaultValue ) );
+
+    if ( mLayer->fields().at( mFieldIdx ).isNumeric() )
+    {
+      mMergePolicyComboBox->addItem( tr( "Use Sum" ), QVariant::fromValue( Qgis::FieldDomainMergePolicy::Sum ) );
+
+      if ( mLayer->geometryType() != Qgis::GeometryType::Point )
+        mMergePolicyComboBox->addItem( tr( "Use Average Weighted by Geometry" ), QVariant::fromValue( Qgis::FieldDomainMergePolicy::GeometryWeighted ) );
+    }
+  }
+  else
+  {
+    mMergePolicyComboBox->setEnabled( false );
+    mMergePolicyLabel->setEnabled( false );
+    mMergePolicyDescriptionLabel->hide();
+  }
+
+  connect( mMergePolicyComboBox, qOverload<int>( &QComboBox::currentIndexChanged ), this, &QgsAttributeTypeDialog::updateMergePolicyLabel );
+  updateMergePolicyLabel();
 }
 
 QgsAttributeTypeDialog::~QgsAttributeTypeDialog()
@@ -400,6 +423,17 @@ void QgsAttributeTypeDialog::setDuplicatePolicy( Qgis::FieldDuplicatePolicy poli
   updateSplitPolicyLabel();
 }
 
+void QgsAttributeTypeDialog::setMergePolicy( Qgis::FieldDomainMergePolicy policy )
+{
+  mMergePolicyComboBox->setCurrentIndex( mMergePolicyComboBox->findData( QVariant::fromValue( policy ) ) );
+  updateMergePolicyLabel();
+}
+
+Qgis::FieldDomainMergePolicy QgsAttributeTypeDialog::mergePolicy() const
+{
+  return mMergePolicyComboBox->currentData().value<Qgis::FieldDomainMergePolicy>();
+}
+
 QString QgsAttributeTypeDialog::constraintExpression() const
 {
   return constraintExpressionWidget->asExpression();
@@ -537,6 +571,30 @@ void QgsAttributeTypeDialog::updateDuplicatePolicyLabel()
   mDuplicatePolicyDescriptionLabel->setText( QStringLiteral( "<i>%1</i>" ).arg( helperText ) );
 }
 
+void QgsAttributeTypeDialog::updateMergePolicyLabel()
+{
+  QString helperText;
+  switch ( mMergePolicyComboBox->currentData().value<Qgis::FieldDomainMergePolicy>() )
+  {
+    case Qgis::FieldDomainMergePolicy::DefaultValue:
+      helperText = tr( "Use default field value." );
+      break;
+
+    case Qgis::FieldDomainMergePolicy::Sum:
+      helperText = tr( "Sum of values." );
+      break;
+
+    case Qgis::FieldDomainMergePolicy::GeometryWeighted:
+      helperText = tr( "New values are computed as the weighted average of the source values." );
+      break;
+
+    case Qgis::FieldDomainMergePolicy::UnsetField:
+      helperText = tr( "Clears the field to an unset state." );
+      break;
+  }
+  mMergePolicyDescriptionLabel->setText( QStringLiteral( "<i>%1</i>" ).arg( helperText ) );
+}
+
 QStandardItem *QgsAttributeTypeDialog::currentItem() const
 {
   QStandardItemModel *widgetTypeModel = qobject_cast<QStandardItemModel *>( mWidgetTypeComboBox->model() );

src/gui/attributeformconfig/qgsattributetypedialog.h

@@ -271,6 +271,24 @@ class GUI_EXPORT QgsAttributeTypeDialog : public QWidget, private Ui::QgsAttribu
      */
     void setDuplicatePolicy( Qgis::FieldDuplicatePolicy policy );
 
+    /**
+     * Returns the field's merge policy.
+     *
+     * \see setMergePolicy()
+     *
+     * \since QGIS 3.42
+     */
+    Qgis::FieldDomainMergePolicy mergePolicy() const;
+
+    /**
+     * Sets the field's merge policy.
+     *
+     * \see mergePolicy()
+     *
+     * \since QGIS 3.42
+     */
+    void setMergePolicy( Qgis::FieldDomainMergePolicy policy );
+
   private slots:
 
     /**
@@ -285,6 +303,8 @@ class GUI_EXPORT QgsAttributeTypeDialog : public QWidget, private Ui::QgsAttribu
 
     void updateDuplicatePolicyLabel();
 
+    void updateMergePolicyLabel();
+
   private:
     QgsVectorLayer *mLayer = nullptr;
     int mFieldIdx;

src/gui/vector/qgsattributesformproperties.cpp

@@ -343,6 +343,7 @@ void QgsAttributesFormProperties::loadAttributeTypeDialogFromConfiguration( cons
   mAttributeTypeDialog->setUniqueEnforced( constraints.constraintStrength( QgsFieldConstraints::ConstraintUnique ) == QgsFieldConstraints::ConstraintStrengthHard );
   mAttributeTypeDialog->setSplitPolicy( config.mSplitPolicy );
   mAttributeTypeDialog->setDuplicatePolicy( config.mDuplicatePolicy );
+  mAttributeTypeDialog->setMergePolicy( config.mMergePolicy );
 
   QgsFieldConstraints::Constraints providerConstraints = QgsFieldConstraints::Constraints();
   if ( constraints.constraintOrigin( QgsFieldConstraints::ConstraintNotNull ) == QgsFieldConstraints::ConstraintOriginProvider )
@@ -417,6 +418,7 @@ void QgsAttributesFormProperties::storeAttributeTypeDialog()
   cfg.mEditorWidgetConfig = mAttributeTypeDialog->editorWidgetConfig();
   cfg.mSplitPolicy = mAttributeTypeDialog->splitPolicy();
   cfg.mDuplicatePolicy = mAttributeTypeDialog->duplicatePolicy();
+  cfg.mMergePolicy = mAttributeTypeDialog->mergePolicy();
 
   const int fieldIndex = mAttributeTypeDialog->fieldIdx();
   mLayer->setDefaultValueDefinition( fieldIndex, QgsDefaultValue( mAttributeTypeDialog->defaultValueExpression(), mAttributeTypeDialog->applyDefaultValueOnUpdate() ) );
@@ -1047,6 +1049,7 @@ void QgsAttributesFormProperties::apply()
     mLayer->setFieldAlias( idx, cfg.mAlias );
     mLayer->setFieldSplitPolicy( idx, cfg.mSplitPolicy );
     mLayer->setFieldDuplicatePolicy( idx, cfg.mDuplicatePolicy );
+    mLayer->setFieldMergePolicy( idx, cfg.mMergePolicy );
   }
 
   // tabs and groups
@@ -1118,6 +1121,7 @@ QgsAttributesFormProperties::FieldConfig::FieldConfig( QgsVectorLayer *layer, in
   mEditorWidgetConfig = setup.config();
   mSplitPolicy = layer->fields().at( idx ).splitPolicy();
   mDuplicatePolicy = layer->fields().at( idx ).duplicatePolicy();
+  mMergePolicy = layer->fields().at( idx ).mergePolicy();
 }
 
 QgsAttributesFormProperties::FieldConfig::operator QVariant()
@@ -2117,6 +2121,11 @@ void QgsAttributesFormProperties::copyWidgetConfiguration()
   duplicatePolicyElement.setAttribute( QStringLiteral( "policy" ), qgsEnumValueToKey( field.duplicatePolicy() ) );
   documentElement.appendChild( duplicatePolicyElement );
 
+  // Merge policy
+  QDomElement mergePolicyElement = doc.createElement( QStringLiteral( "mergePolicy" ) );
+  mergePolicyElement.setAttribute( QStringLiteral( "policy" ), qgsEnumValueToKey( field.mergePolicy() ) );
+  documentElement.appendChild( mergePolicyElement );
+
   // Default expressions
   QDomElement defaultElem = doc.createElement( QStringLiteral( "default" ) );
   defaultElem.setAttribute( QStringLiteral( "expression" ), field.defaultValueDefinition().expression() );
@@ -2246,6 +2255,14 @@ void QgsAttributesFormProperties::pasteWidgetConfiguration()
       config.mDuplicatePolicy = policy;
     }
 
+    // Merge policy
+    const QDomElement mergePolicyElement = docElem.firstChildElement( QStringLiteral( "mergePolicy" ) );
+    if ( !mergePolicyElement.isNull() )
+    {
+      const Qgis::FieldDomainMergePolicy policy = qgsEnumKeyToValue( mergePolicyElement.attribute( QStringLiteral( "policy" ) ), Qgis::FieldDomainMergePolicy::DefaultValue );
+      config.mMergePolicy = policy;
+    }
+
     // Default expressions
     const QDomElement defaultElement = docElem.firstChildElement( QStringLiteral( "default" ) );
     if ( !defaultElement.isNull() )

src/gui/vector/qgsattributesformproperties.h

@@ -374,6 +374,7 @@ class GUI_EXPORT QgsAttributesFormProperties : public QWidget, public QgsExpress
         QString mComment;
         Qgis::FieldDomainSplitPolicy mSplitPolicy = Qgis::FieldDomainSplitPolicy::Duplicate;
         Qgis::FieldDuplicatePolicy mDuplicatePolicy = Qgis::FieldDuplicatePolicy::Duplicate;
+        Qgis::FieldDomainMergePolicy mMergePolicy = Qgis::FieldDomainMergePolicy::DefaultValue;
 
         operator QVariant();
     };

src/ui/attributeformconfig/qgsattributetypeedit.ui

@@ -284,19 +284,6 @@
       <string>Policies</string>
      </property>
      <layout class="QGridLayout" name="gridLayout_4">
-      <item row="0" column="1" colspan="3">
-       <widget class="QComboBox" name="mSplitPolicyComboBox"/>
-      </item>
-      <item row="4" column="0">
-       <widget class="QLabel" name="mDuplicatePolicyLabel">
-        <property name="text">
-         <string>When duplicating features</string>
-        </property>
-       </widget>
-      </item>
-      <item row="4" column="1" colspan="3">
-       <widget class="QComboBox" name="mDuplicatePolicyComboBox"/>
-      </item>
       <item row="0" column="0">
        <widget class="QLabel" name="mSplitPolicyLabel">
         <property name="text">
@@ -304,6 +291,9 @@
         </property>
        </widget>
       </item>
+      <item row="4" column="1" colspan="3">
+       <widget class="QComboBox" name="mDuplicatePolicyComboBox"/>
+      </item>
       <item row="5" column="0" colspan="4">
        <widget class="QLabel" name="mDuplicatePolicyDescriptionLabel">
         <property name="text">
@@ -314,6 +304,26 @@
         </property>
        </widget>
       </item>
+      <item row="6" column="1" colspan="3">
+       <widget class="QComboBox" name="mMergePolicyComboBox"/>
+      </item>
+      <item row="6" column="0">
+       <widget class="QLabel" name="mMergePolicyLabel">
+        <property name="text">
+         <string>When merging features</string>
+        </property>
+       </widget>
+      </item>
+      <item row="4" column="0">
+       <widget class="QLabel" name="mDuplicatePolicyLabel">
+        <property name="text">
+         <string>When duplicating features</string>
+        </property>
+       </widget>
+      </item>
+      <item row="0" column="1" colspan="3">
+       <widget class="QComboBox" name="mSplitPolicyComboBox"/>
+      </item>
       <item row="1" column="0" colspan="4">
        <widget class="QLabel" name="mSplitPolicyDescriptionLabel">
         <property name="text">
@@ -324,6 +334,13 @@
         </property>
        </widget>
       </item>
+      <item row="7" column="0" colspan="4">
+       <widget class="QLabel" name="mMergePolicyDescriptionLabel">
+        <property name="text">
+         <string>TextLabel</string>
+        </property>
+       </widget>
+      </item>
      </layout>
     </widget>
    </item>