Plain table migration source plugin

Table.php

<?php

namespace Drupal\sd8_migration\Plugin\migrate\source;


use Drupal\migrate\Plugin\migrate\source\SqlBase;

/**
 * Table source from database.
 *
 * @MigrateSource(
 *   id = "sd8_table",
 *   source_module = "sd8"
 * )
 */
class Table extends SqlBase {

  /**
   * @return \Drupal\Core\Database\Query\SelectInterface
   */
  public function query() {
    $query = $this->select($this->configuration['table'], 't')
      ->fields('t');
    foreach (array_keys($this->getIds()) as $id) {
      $query->orderBy($id);
    }
    return $query;
  }

  /**
   * {@inheritdoc}
   */
  public function getIds() {
    if (isset($this->configuration['ids'])) {
      return $this->configuration['ids'];
    }
    /** @var \Drupal\Core\Database\Query\SelectInterface $query */
    $query = $this->select('INFORMATION_SCHEMA.KEY_COLUMN_USAGE', 'i')
      ->fields('i', ['COLUMN_NAME'])
      ->where('TABLE_SCHEMA = SCHEMA()')
      ->condition('TABLE_NAME ', $this->configuration['table'])
      ->condition('CONSTRAINT_NAME', 'PRIMARY');
    // JOINing in INFORMATION_SCHEMA is hideously slow.
    foreach ($query->orderBy('ORDINAL_POSITION')->execute() as $result) {
      $id = $result['COLUMN_NAME'];
      $type = $this->select('INFORMATION_SCHEMA.COLUMNS', 'c')
        ->fields('c', ['DATA_TYPE'])
        ->where('TABLE_SCHEMA = SCHEMA()')
        ->condition('TABLE_NAME ', $this->configuration['table'])
        ->condition('COLUMN_NAME', $id)
        ->execute()
        ->fetchField();
      $ids[$id]['type'] = $type === 'int' ? 'integer' : 'string';
      $ids[$id]['alias'] = 't';
    }
    return $ids;
  }

  /**
   * {@inheritdoc}
   */
  public function fields() {
    return [];
  }

}