Form configureOptions() setting data class

Question

Assume the following code:

class MyInventory extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('uom')
            ->add('min')
            ->add('max')
            ->add('price')
            ->add('number')
            ->add('description')
        ;
    }

    /**
     * @param OptionsResolver $resolver
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'MyCompany\MyBundle\Entity\Inventory'
        ));
    }
}

What is the purpose of setting the "data_class" to a string namespace/classname of the entity in question? Why not instantiate the entity and inject it? I assume the form class now magically does this for you - but could the same thing be achieved (albeit a bit clearer or according to Symfony spec) through services and DiC?

Just curious???

Answer 1

My guess is Symfony Forms will load class metadata, so it can perform validation and data copying later on. It doesn't really need an instance - just the metadata.