Doctrine Populator: Don't clean entity manager

Summary

I have 2 entitys. They have a ManyToOne relationship. When I seed the DB I get an error, that the entity manager thinks there are non-persisted entities.

Versions

	Version
PHP	7.4.5
`fzaninotto/faker`	1.9.1

Self-enclosed code snippet for reproduction

$generator = \Faker\Factory::create('de_DE');
$populator = new Populator($generator, self::entityManger());
$populator->addEntity(AccountType::class, 2);
$populator->addEntity(AccountClass::class, 10);
$inserted = $populator->execute();

Expected output

2 AccountTypes are persisted and 10 AccountClasses with relationships of AccountType

Actual output

1) MtTestCase::testSeeder
Doctrine\ORM\ORMInvalidArgumentException: Multiple non-persisted new entities were found through the given association graph:

 * A new entity was found through the relationship 'App\AccountClass\AccountClass#accountType' that was not configured to cascade persist operations for entity: App\AccountType\AccountType@00000000615169460000000030020730. To solve this issue: Either explicitly call EntityManager#persist() on this unknown entity or configure cascade persist this association in the mapping for example @ManyToOne(..,cascade={"persist"}). If you cannot find out which entity causes the problem implement 'App\AccountType\AccountType#__toString()' to get a clue.

Explanation

In Doctrine\Populator::execute() Line 105 the entity manager is cleaned after each entity class. That means, the populator persists AccountType and that works. But now it cleans the entity manager before creating and persisting AccountClasses. The Populator uses the before inserted AccountTypes correctly, but the entity manage does not know them and thinks they are not persisted.

Our Doctrine Relationship is not set up to cascade:persist, hence Doctrine does not persist (again) the AccountType objects and the error is thrown.

If I comment line 105 everything works fine.

Does anyone know a workaround? Or may I start a PR to handle the cleaning differntly. For example with a flag to clean after everything is persisted.

fzaninotto / Faker