Issue #2944437 by quiron, heddn: Provide an entity lookup plugin with support...

Issue #2944437 by quiron, heddn: Provide an entity lookup plugin with support for default lookup value

src/Plugin/migrate/process/DefaultEntityValue.php

+<?php
+
+namespace Drupal\migrate_plus\Plugin\migrate\process;
+
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Row;
+
+/**
+ * Returns EntityLookup for a given default value if input is empty.
+ *
+ * @see \Drupal\migrate_plus\Plugin\migrate\process\EntityLookup
+ *
+ * Example usage with full configuration:
+ * @code
+ * process:
+ *   uid:
+ *     -
+ *       plugin: migration_lookup
+ *       migration: users
+ *       source: author
+ *     -
+ *       plugin: default_entity_value
+ *       entity_type: user
+ *       value_key: name
+ *       ignore_case: true
+ *       default_value: editorial
+ * @endcode
+ *
+ * @MigrateProcessPlugin(
+ *   id = "default_entity_value",
+ *   handle_multiples = TRUE
+ * )
+ */
+class DefaultEntityValue extends EntityLookup {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    if (!empty($value)) {
+      return $value;
+    }
+    return parent::transform($this->configuration['default_value'], $migrate_executable, $row, $destination_property);
+  }
+
+}

tests/src/Kernel/Plugin/migrate/process/DefaultEntityValueTest.php

+<?php
+
+namespace Drupal\Tests\migrate_plus\Kernel\Plugin\migrate\process;
+
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\MigrateDestinationInterface;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\Row;
+use Drupal\Tests\user\Traits\UserCreationTrait;
+
+/**
+ * Tests the default_entity_value plugin.
+ *
+ * @coversDefaultClass \Drupal\migrate_plus\Plugin\migrate\process\DefaultEntityValue
+ * @group migrate_plus
+ */
+class DefaultEntityValueTest extends KernelTestBase {
+
+  use UserCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = [
+    'migrate_plus',
+    'migrate',
+    'user',
+    'system',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->installSchema('system', ['sequences']);
+    $this->installEntitySchema('user');
+  }
+
+  /**
+   * Tests the lookup when the value is empty.
+   *
+   * @covers ::transform
+   */
+  public function testDefaultEntityValue() {
+    // Create a user.
+    $editorial_user = $this->createUser([], 'editorial');
+    $journalist_user = $this->createUser([], 'journalist');
+    // Setup test migration objects.
+    $migration_prophecy = $this->prophesize(MigrationInterface::class);
+    $migrate_destination_prophecy = $this->prophesize(MigrateDestinationInterface::class);
+    $migrate_destination_prophecy->getPluginId()->willReturn('user');
+    $migrate_destination = $migrate_destination_prophecy->reveal();
+    $migration_prophecy->getDestinationPlugin()->willReturn($migrate_destination);
+    $migration_prophecy->getProcess()->willReturn([]);
+    $migration = $migration_prophecy->reveal();
+    $configuration = [
+      'entity_type' => 'user',
+      'value_key' => 'name',
+      'ignore_case' => TRUE,
+      'default_value' => 'editorial',
+    ];
+    $plugin = \Drupal::service('plugin.manager.migrate.process')
+      ->createInstance('default_entity_value', $configuration, $migration);
+    $executable = $this->prophesize(MigrateExecutableInterface::class)->reveal();
+    $row = new Row();
+    // Check the case default value is not used.
+    $value = $plugin->transform($journalist_user->id(), $executable, $row, 'name');
+    $this->assertSame($journalist_user->id(), $value);
+    // Check the default value is found.
+    $value = $plugin->transform('', $executable, $row, 'name');
+    $this->assertSame($editorial_user->id(), $value);
+  }
+
+}