Symfony form - how to add some logic while validating - php

Question

I have a form, used for a course subscription, in which I have 2 entity fields, activite and etudiant. I would like NOT to validate this form IF the trainer i already booked (information that i can find in the DB through the entity activite).
How (where...) can i add some logic instructions to control the validation of this form?
Is anybody has an idea? A lead? It would be so simple WITHOUT Symfony (for me)!...
Thanks
class InscriptionType extends AbstractType
{
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('activiteId', 'entity',
array('label'=>'Activité',
'attr'=>array('class'=>'form-control'),
'class'=>'AssoFranceRussie\MainBundle\Entity\Activite',
'property'=>'nomEtNiveauEtJour',
))
->add('etudiantId', 'entity',array('label'=>'Etudiant',
'attr'=>array('class'=>'form-control'),
'class'=>'AssoFranceRussie\MainBundle\Entity\Etudiant',
'property'=>'NomEtPrenom',
))
;
}

Answer 1

You can write your own constraints and validators by extending the Symfony validation classes.
You need to extend Symfony\Component\Validator\Constraint to define the constraint and Symfony\Component\Validator\ConstraintValidator to define the validation code.
There are probably other ways to do this as well, but this gives you complete control of the validation.

Answer 2

You could do what you want in this way:
1- You need a variable to store the EntityManager in your InscriptionType class:
protected $em;
public function __construct($em) {
$this->em = $em;
}
2- Pass the entity manager to the FormType class from your controller as below:
new InscriptionType( $this->getDoctrine()->getManager() );
3- Add the logic what you want in the setDefaultOptions function to specify the validation_groups what you want for the form:
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
$p = $this->em->getRepository('YourBundle:YourEntity')->find(1);
if($p){
$resolver->setDefaults(array(
'data_class' => 'YourBundle\Entity\YourEntity',
'validation_groups' => array('myValidation1'),
'translation_domain'=>'custom'
));
}
else{
$resolver->setDefaults(array(
'data_class' => 'YourBundle\Entity\YourEntity',
'validation_groups' => array('myValidation2'),
'translation_domain'=>'custom'
));
}
}
4- In your entity, you need to specify the validation groups for the fields of the entity:
/**
* #var string
*
* #ORM\Column(name="name", type="string", length=255)
* #Assert\NotNull(groups={"myValidation1"})
*/
private $name;
/**
* #var date
*
* #ORM\Column(name="start", type="date")
* #Assert\NotNull(groups={"myValidation1", "myValidation2"})
* #Assert\Date()
*/
private $start;
In this case, the field 'start' would be validated in both cases, but the first only with the myValidation1 is the group to be validated.
In this way, you could control which fields you want to validate.