Obtaining a given item in a Doctrine ArrayCollection - php

Question

Developing an API where at the start of every request, the provided API key is used to obtain the Account object which is associated with the request.
$account = $em->getRepository(Entity\Account\Account::class)
->findOneBy(['mainKey'=>$request->getHeaderLine('X-API-Key')]);
This Account entity contains a User's ArrayCollection where each of the User entities contains an username property which is unique for a given Account.
Given the username, how can I obtain the User entity? I can do something like the following, however, feel I should be doing differently.
$user = $em->getRepository(Entity\Account\User::class)
->findOneBy(['accountId'=>$account->getId(), 'username'=>'John.Doe']);
Thanks,
PS. I assume that findOneBy() is using a prepared statement behind the scenes and isn't subject to SQL injection, right?
PSS. I just assumed that an ArrayCollection holds a group of objects, but looking at some of the docs, am now not certain.

Answer 1

If Account is related to User (I suppose it is one-to-one), then Account should have $user property defined. And you can access it kinda:
$user = $account->getUser();
Where getUser is:
public function getUser()
{
return $this->user;
}

Answer 2

Both of these approaches seem to work:
$criteria = \Doctrine\Common\Collections\Criteria::create()
->where(\Doctrine\Common\Collections\Criteria::expr()->eq("username", $username));
$user = $users->matching($criteria)->current();
$expr = new \Doctrine\Common\Collections\Expr\Comparison('username', '=', $username);
$criteria = new \Doctrine\Common\Collections\Criteria();
$criteria->where($expr);
$user = $users->matching($criteria)->current();