3 files changed, 215 insertions, 0 deletions

diff --git a/core/modules/migrate/src/Row.php b/core/modules/migrate/src/Row.php
index 3d961902bcd..2b5e8b2fb4e 100644
--- a/core/modules/migrate/src/Row.php
+++ b/core/modules/migrate/src/Row.php
@@ -267,6 +267,32 @@ class Row {
   }
 
   /**
+   * Tests if a property is an empty destination.
+   *
+   * @param string $property
+   *   The name of the property.
+   *
+   * @return bool
+   *   TRUE if the property is an empty destination.
+   */
+  public function hasEmptyDestinationProperty(string $property): bool {
+    return in_array($property, $this->emptyDestinationProperties);
+  }
+
+  /**
+   * Removes an empty destination property.
+   *
+   * @param string $property
+   *   The name of the empty destination property.
+   */
+  public function removeEmptyDestinationProperty(string $property): void {
+    $this->emptyDestinationProperties = array_diff(
+      $this->emptyDestinationProperties,
+      [$property],
+    );
+  }
+
+  /**
    * Returns the whole destination array.
    *
    * @return array
diff --git a/core/modules/migrate/tests/src/Kernel/RowTest.php b/core/modules/migrate/tests/src/Kernel/RowTest.php
new file mode 100644
index 00000000000..1b4adf181c8
--- /dev/null
+++ b/core/modules/migrate/tests/src/Kernel/RowTest.php
@@ -0,0 +1,152 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\migrate\Kernel;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\migrate\Event\MigratePreRowSaveEvent;
+use Drupal\migrate\Event\MigrateEvents;
+use Drupal\migrate\MigrateExecutable;
+use Drupal\migrate\Plugin\MigrationPluginManagerInterface;
+use Symfony\Component\EventDispatcher\EventDispatcherInterface;
+
+/**
+ * Tests the Row class.
+ *
+ * @group migrate
+ */
+class RowTest extends KernelTestBase {
+
+  /**
+   * The event dispatcher.
+   */
+  protected EventDispatcherInterface $eventDispatcher;
+
+  /**
+   * The entity type manager.
+   */
+  protected EntityTypeManagerInterface $entityTypeManager;
+
+  /**
+   * The migration manager.
+   */
+  protected MigrationPluginManagerInterface $migrationManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'entity_test',
+    'field',
+    'migrate',
+    'user',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('entity_test');
+
+    $this->eventDispatcher = \Drupal::service('event_dispatcher');
+    $this->entityTypeManager = \Drupal::service('entity_type.manager');
+    $this->migrationManager = \Drupal::service('plugin.manager.migration');
+
+    // Create two fields that will be set during migration.
+    $fields = ['field1', 'field2'];
+    foreach ($fields as $field) {
+      $this->entityTypeManager->getStorage('field_storage_config')->create([
+        'entity_type' => 'entity_test',
+        'field_name' => $field,
+        'type' => 'string',
+      ])->save();
+      $this->entityTypeManager->getStorage('field_config')->create([
+        'entity_type' => 'entity_test',
+        'field_name' => $field,
+        'bundle' => 'entity_test',
+      ])->save();
+    }
+  }
+
+  /**
+   * Tests the destination properties of the Row class.
+   */
+  public function testRowDestinations(): void {
+    $storage = $this->entityTypeManager->getStorage('entity_test');
+
+    // Execute a migration that creates an entity with two fields.
+    $data_rows = [
+      ['id' => 1, 'field1' => 'f1value', 'field2' => 'f2value'],
+    ];
+    $ids = ['id' => ['type' => 'integer']];
+    $definition = [
+      'source' => [
+        'plugin' => 'embedded_data',
+        'data_rows' => $data_rows,
+        'ids' => $ids,
+      ],
+      'process' => [
+        'id' => 'id',
+        'field1' => 'field1',
+        'field2' => 'field2',
+      ],
+      'destination' => ['plugin' => 'entity:entity_test'],
+    ];
+    $this->executeMigrationImport($definition);
+    $entity = $storage->load(1);
+    $this->assertEquals('f1value', $entity->get('field1')->getValue()[0]['value']);
+    $this->assertEquals('f2value', $entity->get('field2')->getValue()[0]['value']);
+
+    // Execute a second migration that attempts to remove both field values.
+    // The event listener prevents the removal of the second field.
+    $data_rows = [
+      ['id' => 1, 'field1' => NULL, 'field2' => NULL],
+    ];
+    $definition['source']['data_rows'] = $data_rows;
+    $this->eventDispatcher->addListener(MigrateEvents::PRE_ROW_SAVE, [$this, 'preventFieldRemoval']);
+    $this->executeMigrationImport($definition);
+
+    // The first field is now empty but the second field is still set.
+    $entity = $storage->load(1);
+    $this->assertTrue($entity->get('field1')->isEmpty());
+    $this->assertEquals('f2value', $entity->get('field2')->getValue()[0]['value']);
+  }
+
+  /**
+   * The pre-row-save event handler for the second migration.
+   *
+   * Checks row destinations and prevents the removal of the second field.
+   *
+   * @param \Drupal\migrate\Event\MigratePreRowSaveEvent $event
+   *   The migration event.
+   * @param string $name
+   *   The event name.
+   */
+  public function preventFieldRemoval(MigratePreRowSaveEvent $event, string $name): void {
+    $row = $event->getRow();
+
+    // Both fields are empty and their existing values will be removed.
+    $this->assertFalse($row->hasDestinationProperty('field1'));
+    $this->assertFalse($row->hasDestinationProperty('field2'));
+    $this->assertTrue($row->hasEmptyDestinationProperty('field1'));
+    $this->assertTrue($row->hasEmptyDestinationProperty('field2'));
+
+    // Prevent removal of field 2.
+    $row->removeEmptyDestinationProperty('field2');
+  }
+
+  /**
+   * Executes a migration import for the given migration definition.
+   *
+   * @param array $definition
+   *   The migration definition.
+   */
+  protected function executeMigrationImport(array $definition): void {
+    $migration = $this->migrationManager->createStubMigration($definition);
+    (new MigrateExecutable($migration))->import();
+  }
+
+}
diff --git a/core/modules/migrate/tests/src/Unit/RowTest.php b/core/modules/migrate/tests/src/Unit/RowTest.php
index 69fce6f7860..7db1a51db43 100644
--- a/core/modules/migrate/tests/src/Unit/RowTest.php
+++ b/core/modules/migrate/tests/src/Unit/RowTest.php
@@ -292,6 +292,43 @@ class RowTest extends UnitTestCase {
   }
 
   /**
+   * Tests checking for and removing destination properties that may be empty.
+   *
+   * @covers ::hasEmptyDestinationProperty
+   * @covers ::removeEmptyDestinationProperty
+   */
+  public function testDestinationOrEmptyProperty(): void {
+    $row = new Row($this->testValues, $this->testSourceIds);
+
+    // Set a destination.
+    $row->setDestinationProperty('nid', 2);
+    $this->assertTrue($row->hasDestinationProperty('nid'));
+    $this->assertFalse($row->hasEmptyDestinationProperty('nid'));
+
+    // Set an empty destination.
+    $row->setEmptyDestinationProperty('a_property_with_no_value');
+    $this->assertTrue($row->hasEmptyDestinationProperty('a_property_with_no_value'));
+    $this->assertFalse($row->hasDestinationProperty('a_property_with_no_value'));
+
+    // Removing an empty destination that is not actually empty has no effect.
+    $row->removeEmptyDestinationProperty('nid');
+    $this->assertTrue($row->hasDestinationProperty('nid'));
+    $this->assertFalse($row->hasEmptyDestinationProperty('nid'));
+
+    // Removing a destination that is actually empty has no effect.
+    $row->removeDestinationProperty('a_property_with_no_value');
+    $this->assertTrue($row->hasEmptyDestinationProperty('a_property_with_no_value'));
+
+    // Remove the empty destination.
+    $row->removeEmptyDestinationProperty('a_property_with_no_value');
+    $this->assertFalse($row->hasEmptyDestinationProperty('a_property_with_no_value'));
+
+    // Removing a destination that does not exist does not throw an error.
+    $this->assertFalse($row->hasEmptyDestinationProperty('not_a_property'));
+    $row->removeEmptyDestinationProperty('not_a_property');
+  }
+
+  /**
    * Tests setting/getting multiple destination IDs.
    */
   public function testMultipleDestination(): void {