FormType - ManyToMany on himself - symfony

Question

I try to do a Parents, Children relation on an Entity, but I've a problem when I submit the form. (It's a ManyToMany on himself)
To do it, I've a ManyToMany relation on my entity like it:
class Strain
{
/**
* #ORM\ManyToMany(targetEntity="AppBundle\Entity\Strain", inversedBy="children")
*/
private $parents;
/**
* #ORM\ManyToMany(targetEntity="AppBundle\Entity\Strain", mappedBy="parents")
*/
private $children;
public function __construct()
{
$this->parents = new ArrayCollection();
$this->children = new ArrayCollection();
}
public function addParent(Strain $strain)
{
$this->parents->add($strain);
}
public function removeParent(Strain $strain)
{
$this->parents->removeElement($strain);
}
public function getParents()
{
return $this->parents;
}
public function getChildren()
{
return $this->children;
}
I think it's okay, I've the foreign keys, an intermediate table strain_strain, with 2 columns: strain_source and strain_target.
My FormTypes:
class StrainType extends AbstractType
{
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder->add('parents', CollectionType::class, array(
'entry_type' => StrainParentType::class,
'allow_add' => true,
'allow_delete' => true,
'by_reference' => false,
'required' => false,
))
;
/**
* #param OptionsResolver $resolver
*/
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'AppBundle\Entity\Strain'
));
}
And the second:
class StrainParentType extends AbstractType
{
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder->add('gmoStrain', EntityType::class, array(
'class' => 'AppBundle\Entity\Strain',
'choice_label' => 'systematicName',
'placeholder' => '-- select a parent --',
'query_builder' => function(EntityRepository $er) {
return $er->createQueryBuilder('strain')
->orderBy('strain.systematicName', 'ASC');
}
))
;
/**
* #param OptionsResolver $resolver
*/
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'AppBundle\Entity\Strain'
));
}
When I send the form, symfony return this error:
Neither the property "strain" nor one of the methods "getStrain()", "strain()", "isStrain()", "hasStrain()", "__get()" exist and have public access in class "AppBundle\Entity\Strain".
If someone have an idea :/ Because I don't know how to do it.
EDIT:
The problem is in the FormType, because I need a Collection of EntityType, I've do 2 FormType, but I can do it in on FormType and use entry_options to define config of EntityType, like this:
class StrainType extends AbstractType
{
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('parents', CollectionType::class, array(
'entry_type' => EntityType::class,
'entry_options' => array(
'class' => 'AppBundle\Entity\Strain',
'choice_label' => 'systematicName',
'placeholder' => '-- select a parent --',
'query_builder' => function(EntityRepository $er) {
return $er->createQueryBuilder('strain')
->orderBy('strain.systematicName', 'ASC');
}
),
'by_reference' => false,
'allow_add' => true,
'allow_delete' => true,
'required' => false,
))
;
}
/**
* #param OptionsResolver $resolver
*/
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'AppBundle\Entity\Strain'
));
}