symfony3 Dynamic Forms How to extend ChoiceType, EntityType and DocumentType to load choices with AJAX.

Example

In Symfony, the built-in ChoiceType (and EntityType or DocumentType extending it), basicaly work with a constant choice list.

If you want to make it work with ajax calls, you have to change them to accept any sumitted extra choices.

• How to start with an empty choice list ?

  When you build your form, just set the choices option to an empty array() :

   namespace AppBundle\Form;
  
   use Symfony\Component\Form\AbstractType;
  
   use Symfony\Component\Form\FormBuilderInterface;
  
   use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
  
   class FooType extends AbstractType
   {
       public function buildForm(FormBuilderInterface $builder, array $options)
       {
           $builder
               ->add('tag', ChoiceType::class, array('choices'=>array()));
       }
   }
  

  So you will get an empty select input, without choices. This solution works for ChoiceType and all of his children (EntityType, DocumentType, ...).

• How to accept submitted new choices :

  To accept the new choices, you have to make them available in the form field choicelist. You can change your form field depending on submitted data with the FormEvent::PRE_SUBMIT event.

  This example show how to do it with a basic ChoiceType :

   namespace AppBundle\Form;
  
   use Symfony\Component\Form\AbstractType;
  
   use Symfony\Component\Form\FormBuilderInterface;
  
   use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
  
   class FooType extends AbstractType
   {
       public function buildForm(FormBuilderInterface $builder, array $options)
       {
           $builder
               ->add('tag', ChoiceType::class, array('choices'=>array()))
           ;
           
           $builder->addEventListener(
               FormEvents::PRE_SUBMIT,
               function(FormEvent $event){
                   // Get the parent form
                   $form = $event->getForm();
                   
                   // Get the data for the choice field
                   $data = $event->getData()['tag'];
                   
                   // Collect the new choices
                   $choices = array();
                   
                   if(is_array($data)){
                       foreach($data as $choice){
                           $choices[$choice] = $choice;
                       }
                   }
                   else{
                       $choices[$data] = $data;
                   }
                   
                   // Add the field again, with the new choices :
                   $form->add('tag', ChoiceType::class, array('choices'=>$choices));
               }
           );
       }
   }
  

  Your submitted choices are now allowed choices and Symfony ChoiceType built-in validation won't reject them anymore.

  If you wan to do the same with a ChoiceType child (EntityType, DocumentType, ...), you have to inject the entityManager or the documentManager and to do the datatransformation when populating the new choices.