ManyToMany inverse relationships need by_reference on form to update

[andrewyager]

As per discussion on #symfony this evening, it should be documented somewhere that when you have a ManyToMany relationship, and you need the inverse to update the ORM model, you need to pass the by_reference option.

https://gist.github.com/3121916 is a good example of setting up this sort of relationship. Then in your form:

<?php

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class UserGroupType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('users', null, array('label'=>'Users', 'by_reference' => false))
...
        ;
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'UserGroup'
        ));
    }

    public function getName()
    {
        ...
    }
}

[Sgoettschkes]

Looking at the cookbook How to Embed a Collection of Forms, I see the by_reference option in Listing 7. Is this enough or do you think we need a more in-depth description of this?

[weaverryan]

I think we should also highlight it - even with a little code tip that points to the actual by_reference docs on that page - in the entity form reference type (http://symfony.com/doc/current/reference/forms/types/entity.html).

If we do that, then I think we're in good shape. This is also related to the still-needed documentation of the addXxx and removeXxx methods in Symfony 2.1 - see #1322 and #1326.

Thanks!

[fredpeaks]

I think this problem still has to be fixed. There is no documentation of the by_reference option in entity form type but the option still exists and is needed to be able to persist manytomany from the inverse side (by_reference has to be false).

[xabbuh]

@fredpeaks This should be covered with #3410.