Drupal 7 course variation source

Course.php

<?php

namespace Drupal\migrate\Plugin\migrate\source;

use Drupal\migrate\Row;
use Drupal\migrate_drupal\Plugin\migrate\source\d7\FieldableEntity;
use Drupal\paragraphs\Plugin\migrate\field\FieldCollection;

/**
 * Drupal 7 course variation source.
 *
 * @MigrateSource(
 *   id = "course_variation",
 *   source_module = "node"
 * )
 */
class CourseVariation extends FieldableEntity {

  /**
   * The join options
   */
  const JOIN1 = '[n].[nid] = [f].[entity_id]';
  /**
   * The join options
   */
  const JOIN2 = '[fc].[item_id] = [f].[field_course_variation_value]';

  /**
   * The join options
   */
  const JOIN3 = '[fcr].[revision_id] = [f].[field_course_variation_revision_id]';

  /**
   * {@inheritdoc}
   */
  public function query() {

    $query = $this->select('node', 'n');
    $query->innerJoin('field_data_field_course_variation', 'f', static::JOIN1);
    $query->innerJoin('field_collection_item', 'fc', static::JOIN2);
    $query->innerJoin('field_collection_item_revision', 'fcr', static::JOIN3);
    $query->condition('n.type', 'course', '=')
      ->fields('n', ['nid', 'title', 'created', 'changed', 'uid'])
      ->fields('f', ['field_course_variation_value', 'field_course_variation_revision_id', 'delta', 'entity_id'])
      ->fields('fc', ['item_id'])
      ->fields('fcr', ['revision_id']);
    return $query;
  }

  /**
   * {@inheritdoc}
   */
  public function prepareRow(Row $row) {
    // Remove field_ prefix for new bundle.
    $bundle = 'field_course_variation';
    $bundle = substr($bundle, FieldCollection::FIELD_COLLECTION_PREFIX_LENGTH);
    $row->setSourceProperty('bundle', $bundle);
    // Get Field API field values.
    $field_names = array_keys($this->getFields('field_collection_item', 'field_course_variation'));
    $item_id = $row->getSourceProperty('item_id');
    $revision_id = $row->getSourceProperty('revision_id');
    foreach ($field_names as $field_name) {
      $value = $this->getFieldValues('field_collection_item', $field_name, $item_id, $revision_id);
      $row->setSourceProperty($field_name, $value);
    }
    return parent::prepareRow($row);
  }

  /**
   * {@inheritdoc}
   */
  public function fields() {
    $fields = [
      'nid' => $this->t('Node ID'),
      'type' => $this->t('Type'),
      'title' => $this->t('Title'),
      'uid' => $this->t('Node authored by (uid)'),
      'created' => $this->t('Created timestamp'),
      'field_course_variation_value' => $this->t('Id course variation'),
      'field_course_variation_revision_id' => $this->t('Revision Id course variation'),
      'entity_id' => $this->t('Nid'),
      'item_id' => $this->t('Item_id'),
      'revision_id' => $this->t('Revision_id'),
    ];
    return $fields;
  }

  /**
   * {@inheritdoc}
   */
  public function getIds() {
    $ids['item_id']['type'] = 'integer';
    $ids['item_id']['alias'] = 'n';
    return $ids;
  }

}