Symfony2 many-to-many does not update inverse side - php

Question

I have the entities: Students and StudyGroups
Everything works fine with Study Groups. I can choose the list of Students belongs to Study Groups, and Doctrine creates the associations.
However when I want to do the same thing from the other side (choose the Study Groups for students), nothing happens.
Here are the important parts of my YAML file configuration
StudyGroups.orm.yml
manyToMany:
students:
targetEntity: Students
inversedBy: studyGroups
cascade: ["persist"]
joinTable:
name: students_study_groups
joinColumns:
study_groups:
referencedColumnName: id
inverseJoinColumns:
students:
referencedColumnName: id
Students.orm.yml
manyToMany:
studyGroups:
targetEntity: StudyGroups
mappedBy: students
cascade: ["persist"]
lifecycleCallbacks: { }
I also tried the following modification in StudyGroups.php entity file
public function addStudent(\AppBundle\Entity\Students $students) {
$students->addStudyGroup($this); // ADDED THIS LINE
$this->students[] = $students;
return $this;
}
Same in Students.php entity file
public function addStudyGroup(\AppBundle\Entity\StudyGroups $studyGroups) {
$studyGroups->addStudent($this); // ADDED THIS LINE
$this->studyGroups[] = $studyGroups;
return $this;
}
The interesting thing I found about this problem, is that if I switch the Inverse and Owning side in StudyGroups.orm.yml and Students.orm.yml the issue will switch too.
I am aware that this is mentioned here: http://doctrine-orm.readthedocs.org/projects/doctrine-orm/en/latest/reference/unitofwork-associations.html
11.2. Important concepts
Changes made only to the inverse side of an association are ignored. Make sure to update both sides of a bidirectional association (or at least the owning side, from Doctrine’s point of view)
This is my problem. My changes to my inverse side are ignored. How can I fix this ? I tried all those things mentioned by other users, but still doesn't work. Thanks in advance.
UPDATE 1
Here is my method for editing Students. Please note that if I switch the inverse and owning side (in the YAML file configuration), the Study Groups editing will work, and the Students editing will not work. (by not work, I mean it does not create the association between the two)
public function editStudentAction(Request $request, $student) {
/* DATABASE SERVICE */
$this->db_helper = $this->get('db.helper');
/* DOCTRINE */
$em = $this->getDoctrine()->getManager();
$student = $em->getRepository('AppBundle:Students')->find($student);
/* INVALID ID */
if (count($student) == 0) {
/* INVALID ID */
$request->getSession()->getFlashBag()->add(
'error', 'Invalid ID!'
);
return $this->redirect($this->generateUrl('index'));
}
/* GET STUDENT FORM */
$form = $this->newStudentForm($student, "edit");
/* HANDLE FORM SUBMISSION */
$form->handleRequest($request);
if ($form->isValid()) {
/* CHECK IF STUDENT ONLY WANT TO ENROLL 2 STUDY GROUPS */
if (count($student->getStudyGroups()) > 2) {
$request->getSession()->getFlashBag()->add(
'error', 'Students may only enroll 2 study groups at the same time!'
);
} else {
try {
/* SAVE TO DATABASE */
$em->persist($student);
$em->flush();
/* REDIRECT TO MAIN PAGE */
return $this->redirect($this->generateUrl('index'));
} catch (\Doctrine\DBAL\DBALException $e) {
/* HANDLE DUPLICATE KEY ISSUE */
if ($e->getPrevious()->getCode() === '23000') {
$request->getSession()->getFlashBag()->add(
'error', 'User already exists!'
);
} else
throw $e;
}
}
}
return $this->render('default/new.html.twig', array(
'form' => $form->createView(),
'object' => "student"
));
}

Answer 1

I'm highly surprised this works either side, as it would appear you have a potential infinite loop happening.
addStudent() calls addStudyGroup() which calls addStudent() which calls addStudyGroup() which calls addStudent()............ Remove those two "ADDED THIS LINE", this needs to happen in your controller.
Here's an update to go in your controller. First you need to remember the existing list of study groups for this student before you create the form:
/* GET ORIGNAL COLLECTIONS */
$originalGroups = new ArrayCollection(); // requires: use Doctrine\Common\Collections\ArrayCollection;
foreach ($student->getStudyGroups() as $group) {
$originalGroups->add($group);
}
/* GET STUDENT FORM */
Now you need to remove any removed study groups from the new collection,
/* MANY TO MANY */
foreach ($originalGroups as $group) {
if (!$student->getStudyGroups()->contains($group)) {
$student->removeStudyGroup($group);
$group->removeStudent($student);
$em->remove($group);
} else {
$group->addStudent($student);
$em->persist($group);
}
}
/* SAVE TO DATABASE */
$em->persist($student);