class QueryFactory

1. 9.x drupal/core/lib/Drupal/Core/Entity/Query/QueryFactory.php \Drupal\Core\Entity\Query\QueryFactory
2. 9.x drupal/core/modules/field/modules/field_sql_storage/lib/Drupal/field_sql_storage/Entity/QueryFactory.php \Drupal\field_sql_storage\Entity\QueryFactory

EfqTest.php in drupal/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/EfqTest.php

Definition of Drupal\taxonomy\Tests\EfqTest.

field.module in drupal/core/modules/field/field.module

Attach custom data fields to Drupal entities.

options.module in drupal/core/modules/field/modules/options/options.module

Defines selection, check box and radio button widgets for text and numeric fields.

class QueryFactory {

  /**
   * var \Symfony\Component\DependencyInjection\ContainerInterface
   */
  protected $container;

  /**
   * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
   */
  function __construct(ContainerInterface $container) {
    $this->container = $container;
  }

  /**
   * @param string $entity_type
   * @param string $conjunction
   * @return QueryInterface
   */
  public function get($entity_type, $conjunction = 'AND') {
    $service_name = entity_get_controller($entity_type)
      ->getQueryServicename();
    return $this->container
      ->get($service_name)
      ->get($entity_type, $conjunction);
  }

}