Persist an entity without attaching it to the EntityManager - doctrine-orm

Question

I want to bulk-import Doctrine entities from an XML file.
The XML file can be very large (up to 1 million entities), so I can't persist all my entities the traditional way:
$em->beginTransaction();
while ($entity = $xmlReader->readNextEntity()) {
$em->persist($entity);
}
$em->flush();
$em->commit();
I would soon exceed my memory limit, and Doctrine is not really designed to handle that many managed entities.
I don't need to track changes to the persisted entities, just to persist them; therefore I don't want them to be managed by the EntityManager.
Is it possible to persist entities without getting them managed by the EntityManager?
The first option that comes to my mind is to detach it immediately after persisting it:
$em->beginTransaction();
while ($entity = $xmlReader->readNextEntity()) {
$em->persist($entity);
$em->flush($entity);
$em->detach($entity);
}
$em->commit();
But this is quite expensive in Doctrine, and would slow down the import.
The other option would be to directly insert the data into the database using the Connection object and a prepared statement, but I like the abstraction of the entity and would ideally like to store the object directly.

Answer 1

Instead of using detach and flush after each insert, you can call clear (which detaches all entities from the manager) and flush in batches, which should be significantly faster:
Bulk inserts in Doctrine are best performed in batches, taking
advantage of the transactional write-behind behavior of an
EntityManager. The following code shows an example for inserting 10000
objects with a batch size of 20. You may need to experiment with the
batch size to find the size that works best for you. Larger batch
sizes mean more prepared statement reuse internally but also mean more
work during flush.
https://doctrine-orm.readthedocs.org/projects/doctrine-orm/en/latest/reference/batch-processing.html
If possible, I recommend avoiding transactions for bulk operations as they tend to slow things down:
//$em->beginTransaction();
$i = 0;
while ($entity = $xmlReader->readNextEntity()) {
$em->persist($entity);
if(++$i % 20 == 0) {
$em->flush();
$em->clear(); // detaches all entities
}
}
$em->flush(); //Persist objects that did not make up an entire batch
$em->clear();
//$em->commit();