Add entity source for easier source querying

While writing a field collections migration, I got tired of digging through my source database looking for where various bits of needed data were stored (across a bunch of tables.) I thought it would be much easier if I could use an entity field query instead of an SQL query as a source. I've added a MigrateSourceEntity plugin to the D7 folder.

This is based on https://www.drupal.org/node/1883112. I opted to add it to migrate_d2d since it really is only applicable for a Drupal(7)-to-Drupal migration.

Here's an example of how I used it for the field collection migration. It's worth noting that this example is overly complicated by some field_collections-specific gotchas; however, the essence of the MigrateSourceEntity's usage is captured in the $this->source() assignment in __construct() and the query() function.

class MyExhibitorRepFieldCollection extends DrupalMigration {

  public function __construct(array $arguments) {
    parent::__construct($arguments);

    $this->source = new MigrateSourceEntity(
      $this->sourceConnection,
      $this->query(),
      $this->sourceFields,
      null,
      [
        'wrap_entity'=> true,
        'source_fields' => [
          'field_rep_email',
          'field_rep_name',
          'field_rep_phone',
        ],
      ]
    );

    $this->destination = new MyMigrateDestinationFieldCollection(
      'field_exhibitor_reps',
      array('host_entity_type' => 'commerce_customer_profile')
    );

    $this->map = new MigrateSQLMap($this->machineName,
      array(
        'id' => array(
          'type' => 'int',
          'unsigned' => TRUE,
          'not null' => TRUE,
        ),
      ),
      MyMigrateDestinationFieldCollection::getKeySchema()
    );

    $this->addFieldMapping('host_entity_id', 'host_entity')
      ->sourceMigration('ExhibitorProfiles');

    $this->addSimpleMappings([
      'field_rep_name',
      'field_rep_phone',
      'field_rep_email',
    ]);

    $this->addUnmigratedDestinations(['path']);

    $this->addUnmigratedSources([
      'item_id',
      'revision_id',
      'field_name',
      'archived',
      'url',
    ]);

  }

  /**
   * The base source query for this migration.
   *
   * @return \EntityFieldQuery
   */
  protected function query() {

    $query = new EntityFieldQuery();
    $query->entityCondition('entity_type', 'field_collection_item');
    $query->entityCondition('bundle', 'field_exhibitor_reps');

    return $query;
  }

  public function prepareRow($row) {
    if (parent::prepareRow($row) == false) {
      return false;
    }

    // This is a bit of a hack, but for some reason the field collection item's
    // hostEntityId() function only returns NULL. Get the host id directly from
    // the source database. The field mapping's sourceMigration property will
    // automatically cross reference this is with the new id from the
    // ExhibitorProfiles migration.
    $result = Database::getConnection('default', $this->sourceConnection)
      ->select('field_data_field_exhibitor_reps', 'f')
      ->fields('f', ['entity_id'])
      ->condition('f.field_exhibitor_reps_value', $row->source->item_id)
      ->condition('f.field_exhibitor_reps_revision_id', $row->source->revision_id)
      ->execute();

    $row->host_entity = $result->fetchField();

    $row->field_rep_email = $row->field_rep_email[LANGUAGE_NONE][0]['email'];
    $row->field_rep_name = $row->field_rep_name[LANGUAGE_NONE][0]['value'];
    $row->field_rep_phone = $row->field_rep_phone[LANGUAGE_NONE][0]['value'];

  }
}

class MyMigrateDestinationFieldCollection extends MigrateDestinationFieldCollection {
  public function import(stdClass $collection, stdClass $row) {
    // MigrateDestinationFieldCollection assumes host_entity_id is a single key
    // Since this customer profiles use compound keys (entity_id & revision_id) use
    // only the first key in the array.
    $collection->host_entity_id = $collection->host_entity_id['destid1'];
    return parent::import($collection, $row);
  }
}