many-to-many checkboxes not checked when they should be - symfony

Question

I have a form with a bunch of many-to-many checkboxes. The form saves just fine (I checked the database to make sure), but then the checkboxes aren't checked in agreement with the database.
Is there something special I need to do to get the checkboxes to stay checked?
Here's my form definition:
<?php
namespace VNN\PressboxBundle\Form;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilder;
class PreferencesSportsICareAboutType extends AbstractType
{
public function buildForm(FormBuilder $builder, array $options)
{
$builder->add('interestingSports', 'entity', array(
'multiple' => true,
'expanded' => true,
'property' => 'name',
'class' => 'VNN\PressboxBundle\Entity\Sport',
'query_builder' => function(\VNN\PressboxBundle\Repository\SportRepository $er) {
return $er->createQueryBuilder('s')
->orderBy('s.name', 'ASC');
},
));
}
public function getName()
{
return 'vnn_pressboxbundle_preferencessportsicareabouttype';
}
}
And here's the relevant part of my template:
{% block form %}
<h2>Sports I Care About</h2>
<form action="{{ path('user_update_preferences', { 'sectionName': sectionName }) }}" method="post" {{ form_enctype(form) }} novalidate class="clearfix">
{% for error in errors %}
error: {{ error.messageTemplate }}
{% endfor %}
{% for field in form.interestingSports %}
<li>
{{ form_widget(field) }}
{{ form_label(field) }}
</li>
{% endfor %}
{{ form_rest(form) }}
<p><button type="submit">Submit</button></p>
</form>
{% endblock %}

Answer 1

It looks like your Type and your Template are well defined. You should check your entity relationships.
I have already implement the same behavior but using a One-To-Many relationship.
Edit by OP:
It was the entity relationships. I needed to change this
/**
* #ORM\ManyToMany(targetEntity="UserSportInterest", inversedBy="sports")
* #JoinTable(name="user_sport_interest",
* joinColumns={#JoinColumn(name="user_id", referencedColumnName="id")},
* inverseJoinColumns={#JoinColumn(name="sport_id", referencedColumnName="id")}
* )
*/
private $sports;
to this (note targetEntity change)
/**
* #ORM\ManyToMany(targetEntity="Sport", inversedBy="sports")
* #JoinTable(name="user_sport_interest",
* joinColumns={#JoinColumn(name="user_id", referencedColumnName="id")},
* inverseJoinColumns={#JoinColumn(name="sport_id", referencedColumnName="id")}
* )
*/
private $sports;
After that, it worked fine.