Symfony 2.7 findOneBy() Function Finds the Wrong Entity - symfony

Question

I've got a controller action that's supposed to be looking for semi-duplicate entries in a collection, and removing them from that Entity's list. New ones should not have an ID yet, and existing ones do, so I'm running findOneBy() with an array of parameters to match on (leaving out ID).
I am baffled and deeply troubled by the error I am getting, where it finds the wrong entity! I've got some relevant code below, I hope this is just a dream or a silly mistake, I can't reproduce the output on my own windows development environment, but my co-worker was testing on his mac, and was getting errors, so I went on his machine and did some quick echoing to see what was going on. See the code and the result below.
CODE
foreach($entity->getTechnicians() as $tech) {
//find new addtions, see if they exist
if (!$tech->getId()) {
echo "Technician " . $tech->getFirstName() . " has no ID, trying to find one that does<br/>";
$found = $em->getRepository('TechnicianBundle:Technician')->findOneBy(array(
'firstName' => $tech->getFirstName(),
'lastName' => $tech->getLastName(),
'email' => $tech->getEmail(),
'residentEngineer' => $tech->getResidentEngineer(),
'officeNumber' => $tech->getOfficeNumber()
));
//if one with an ID already exists
if ($found) {
echo "found technician " . $found->getFirstName() . " that already has id " . $found->getId() . "<br/>";
...
OUTPUT
Technician Four has no ID, trying to find one that does
found technician khjvuov that already has id 7

Answer 1

Probably it's not a findOneBy() issue.
If without add/remove calls it works, it may be caused by modified current pointer of ArrayCollection so when $tech->getFirstName() is called it actually points to another entry.
You may try to iterate your collection like this:
$iterator = $entity->getTechnicians()->getIterator();
while ($iterator->valid()) {
$tech = $iterator->current();
... $entity->addTechnician()/$entity->removeTechnician()
$iterator->next();
}
It will create new ArrayIterator object, so you can modify underlying object preserving ArrayCollection's internal pointer.
This may be obsolete if you are running PHP7 (reference - Note box)

Answer 2

Ultimately, the findOneBy() method uses the load() method of the Doctrine ORM.
In the doc, the parameter $criteria is described as such :
#param array $criteria The criteria by which to load the entity.
You should probably dig deeper into Doctrine API to make sure, but there is a big chance that in the array you are passing as an argument, only the first key => value pair is taken into account (in your example, 'firstName' => $tech->getFirstName()).
If this is the case, you'll probably need to add your own custom method in your entity repository, one that would allow you to query your database with more advanced statements (using OR/AND or LIKE() in SQL for instance).