getEntityTypeMigrationId example

  abstract protected function entityId();

  /** * {@inheritdoc} */
  public function alterFieldInstanceMigration(MigrationInterface $migration) {
    parent::alterFieldInstanceMigration($migration);

    // Add the reference migration as a required dependency to this migration.     $migration_dependencies = $migration->getMigrationDependencies(TRUE);
    array_push($migration_dependencies['required'], $this->getEntityTypeMigrationId());
    $migration_dependencies['required'] = array_unique($migration_dependencies['required']);
    $migration->set('migration_dependencies', $migration_dependencies);
  }

  /** * {@inheritdoc} */
  public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {
    $process = [
      'plugin' => 'sub_process',
      'source' => $field_name,