Symfony2 Forms and Polymorphic collections

Question

Im playing around with Symfony2 and Im abit unsure how Symfony2 handles Polymorphic collections in the View component. It seems that i can create an entity with a collection of AbstractChildren, but not sure how to what to do with it inside a Form Type class.

For example, I have the following entity relationship.

/**
 * @ORM\Entity
 */
class Order
{
    /**
     * @ORM\OneToMany(targetEntity="AbstractOrderItem", mappedBy="order", cascade={"all"}, orphanRemoval=true)
     * 
     * @var AbstractOrderItem $items;
     */
    $orderItems;  
    ...
}


/**
 * Base class for order items to be added to an Order
 *
 * @ORM\Entity
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="discr", type="string")
 * @ORM\DiscriminatorMap({
 *     "ProductOrderItem" = "ProductOrderItem",
 *     "SubscriptionOrderItem " = "SubscriptionOrderItem "
 * })
 */
class AbstractOrderItem
{
    $id;
    ...
}

/**
 * @ORM\Entity
 */
class ProductOrderItem  extends AbstractOrderItem
{
    $productName;
}

/**
 * @ORM\Entity
 */
class SubscriptionOrderItem extends AbstractOrderItem
{
    $duration;
    $startDate;
    ...
}

Simple enough, but when im create a form for my order class

class OrderType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder->add('items', 'collection', array('type' => AbstractOrderItemType()));
    }
}

I am unsure how to handle this situation where you effectively need a different Form Type for each class of item in the collection?

Answer 1

I recently tackled a similar problem - Symfony itself makes no concessions for polymorphic collections, but it's easy to provide support for them using an EventListener to extend the form.

Below is the content of my EventListener, which uses a similar approach to Symfony\Component\Form\Extension\Core\EventListener\ResizeFormListener, the event listener which provides the collection form type's normal functionality:

namespace Acme\VariedCollectionBundle\EventListener;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Form\FormFactoryInterface;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;

class VariedCollectionSubscriber implements EventSubscriberInterface
{
    protected $factory;
    protected $type;
    protected $typeCb;
    protected $options;

    public function __construct(FormFactoryInterface $factory, $type, $typeCb)
    {
        $this->factory = $factory;
        $this->type = $type;
        $this->typeCb = $typeCb;
    }

    public static function getSubscribedEvents()
    {
        return array(
            FormEvents::PRE_SET_DATA => 'fixChildTypes'
        );
    }

    public function fixChildTypes(FormEvent $event)
    {
        $form = $event->getForm();
        $data = $event->getData();

        // Go with defaults if we have no data
        if($data === null || '' === $data)
        {
            return;
        }

        // It's possible to use array access/addChild, but it's not a part of the interface
        // Instead, we have to remove all children and re-add them to maintain the order
        $toAdd = array();
        foreach($form as $name => $child)
        {
            // Store our own copy of the original form order, in case any are missing from the data
            $toAdd[$name] = $child->getConfig()->getOptions();
            $form->remove($name);
        }
        // Now that the form is empty, build it up again
        foreach($toAdd as $name => $origOptions)
        {
            // Decide whether to use the default form type or some extension
            $datum = $data[$name] ?: null;
            $type = $this->type;
            if($datum)
            {
                $calculatedType = call_user_func($this->typeCb, $datum);
                if($calculatedType)
                {
                    $type = $calculatedType;
                }
            }
            // And recreate the form field
            $form->add($this->factory->createNamed($name, $type, null, $origOptions));
        }
    }
}

The downside to using this approach is that for it to recognize the types of your polymorphic entities on submit, you must set the data on your form with the relevant entities before binding it, otherwise the listener has no way of ascertaining what type the data really is. You could potentially work around this working with the FormTypeGuesser system, but that was beyond the scope of my solution.

Similarly, while a collection using this system still supports adding/removing rows, it will assume that all new rows are of the base type - if you try to set them up as extended entities, it'll give you an error about the form containing extra fields.

For simplicity's sake, I use a convenience type to encapsulate this functionality - see below for that and an example:

namespace Acme\VariedCollectionBundle\Form\Type;

use Acme\VariedCollectionBundle\EventListener\VariedCollectionSubscriber;
use JMS\DiExtraBundle\Annotation\FormType;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\AbstractType;

/**
 * @FormType()
 */
class VariedCollectionType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        // Tack on our event subscriber
        $builder->addEventSubscriber(new VariedCollectionSubscriber($builder->getFormFactory(), $options['type'], $options['type_cb']));
    }

    public function getParent()
    {
        return "collection";
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setRequired(array('type_cb'));
    }

    public function getName()
    {
        return "varied_collection";
    }
}

Example: namespace Acme\VariedCollectionBundle\Form;

use Acme\VariedCollectionBundle\Entity\TestModelWithDate;
use Acme\VariedCollectionBundle\Entity\TestModelWithInt;
use JMS\DiExtraBundle\Annotation\FormType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\AbstractType;

/**
 * @FormType()
 */
class TestForm extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $typeCb = function($datum) {
            if($datum instanceof TestModelWithInt)
            {
                return "test_with_int_type";
            }
            elseif($datum instanceof TestModelWithDate)
            {
                return "test_with_date_type";
            }
            else
            {
                return null; // Returning null tells the varied collection to use the default type - can be omitted, but included here for clarity
            }
        };

        $builder->add('demoCollection', 'varied_collection', array('type_cb' => $typeCb,  /* Used for determining the per-item type */
                                                                   'type' => 'test_type', /* Used as a fallback and for prototypes */
                                                                   'allow_add' => true,
                                                                   'allow_remove' => true));
    }

    public function getName()
    {
        return "test_form";
    }
}