How to configure Empty Data for a Form Class

The empty_data option allows you to specify an empty data set for your form class. This empty data set would be used if you bind your form, but haven’t called setData() on your form or passed in data when you created you form. Por ejemplo:

public function indexAction()
{
    $blog = // ...

    // $blog is passed in as the data, so the empty_data option is not needed
    $form = $this->createForm(new BlogType(), $blog);

    // no data is passed in, so empty_data is used to get the "starting data"
    $form = $this->createForm(new BlogType());
}

By default, empty_data is set to null. Or, if you have specified a data_class option for your form class, it will default to a new instance of that class. That instance will be created by calling the constructor with no arguments.

If you want to override this default behavior, there are two ways to do this.

Option 1: Instantiate a new Class

One reason you might use this option is if you want to use a constructor that takes arguments. Remember, the default data_class option calls that constructor with no arguments:

// src/Acme/DemoBundle/Form/Type/BlogType.php
// ...

use Symfony\Component\Form\AbstractType;
use Acme\DemoBundle\Entity\Blog;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class BlogType extends AbstractType
{
    private $someDependency;

    public function __construct($someDependency)
    {
        $this->someDependency = $someDependency;
    }
    // ...

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'empty_data' => new Blog($this->someDependency),
        ));
    }
}

You can instantiate your class however you want. In this example, we pass some dependency into the BlogType when we instantiate it, then use that to instantiate the Blog object. The point is, you can set empty_data to the exact “new” object that you want to use.

Option 2: Provide a Closure

Using a closure is the preferred method, since it will only create the object if it is needed.

The closure must accept a FormInterface instance as the first argument:

use Symfony\Component\OptionsResolver\OptionsResolverInterface;
use Symfony\Component\Form\FormInterface;
// ...

public function setDefaultOptions(OptionsResolverInterface $resolver)
{
    $resolver->setDefaults(array(
        'empty_data' => function (FormInterface $form) {
            return new Blog($form->get('title')->getData());
        },
    ));
}