Proper way to update bidirectional Many to Many relationship symfony2-doctrine

Question

I did some research, and after reading this and this (and all the related questions) I still can\'t figure which is the proper way to update a many to many relationship in S

Answer 1

ManyToMany Bidirectional with indexBy attribute on the annotation fixed this for me

Student class annotation should be

class student_main
{
    /**
     * @ORM\ManyToMany(targetEntity="support_log", mappedBy="student_main")
     **/
    private $support_log;

Support class annotation should be

    class support_log
    {
        /**
         * @ORM\ManyToMany(targetEntity="student_main", inversedBy="support_log", indexBy="id")
         * @ORM\JoinTable(name="support_log_student",
         *  joinColumns={@ORM\JoinColumn(name="support_log_id",referencedColumnName="id")},
         *  inverseJoinColumns={@ORM\JoinColumn(name="student_id", referecedColumnName="id")}
         * )
         **/            
        private $student;

Now the symfony 2 Form should be

    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder
        ->add('student', 'entity', array(
                'class' => '<>\Entity\Student',
                'property' => 'Name', //property you want to display on the select box
                'label' => 'Belongs to Students',
                'multiple' => true,
                'constraints' => array(
                    new NotBlank(array('message' => 'Please choose atleast one student'))
                )
            ))
        ....
        ;
    }

On submit of form usually inside the Action

        if ($editForm->isValid()) {
            $entity = $editForm->getData(); 
            $em->persist($entity); //this should take care of everything saving the manyToMany records 
            $em->flush();
            return $this->redirect($this->generateUrl('support_log_edit', array('id' => $id)));
        }           

Please note: I haven't tested this code. I rewrote this code to fit the scenario mentioned in the question.