I can't create multiple object of an entity at once - symfony

Question

I'm learning Symfony and I have a situation where I need, after a form, to create multiple object of an entity A.
All these objects are quite identical but just the value of one field change which is a relation OneToMany to an entity B. In the form this relation is selected with checkbox (that are EntityType related to B), and so I want to create one object A for each checked boxes.
My issue is that the First's form allows me to create only one object of First type at a time.
It is a project given by my teachers, and I mustn't create a ManyToMany relation.
Can somebody help me?
Here is the code in the Controller:
$A = new A();
$form = $this->createForm(AType::class, $A);
$form->handleRequest($request);
if ($form->isSubmitted() && $form->isValid()) {
$entityManager = $this->getDoctrine()->getManager();
$entityManager->persist($A);
$entityManager->flush();
}
And here is the code in the FormType:
$builder
->add('anotherField')
->add('idB', EntityType::class, [
'label' => 'B',
'class' => B::class,
'expanded' => true,
'multiple' => true
])
;

Answer 1

If I understand you correctly, with one form submission you wish to save multiple entities to the database. I would clone all the form data into a new object, make changes and then persist all and flush like so:
if ($form->isSubmitted() && $form->isValid()) {
$original = $form->getData();
$copy = clone $original;
// here you can make changes to your copy.
$entityManager = $this->getDoctrine()->getManager();
$entityManager->persist($original);
$entityManager->persist($copy);
$entityManager->flush();
}