[Form] Document "class constraints" for data class-less forms

[PrOF-kk]

Symfony supports using a Form without using a Data Class.
In that page it mentions how to validate individual fields using a constraint, however it's also possible to add constraints to the root form:

• In the controller ->

$form = $this
    ->createFormBuilder(null, [
        'constraints' => [
            new Expression([
                'expression' => 'value["firstName"] == "john"',
            ])
        ]
    ])
    ->add('firstName')
    ->add('lastName')
    ->getForm();

(src)

• In the FormType using configureOptions ->

public function configureOptions(OptionsResolver $resolver)
{
    $collectionConstraint = new Collection(array(
        'CardNumber' => array(
            new Assert\CardScheme(array(
                'schemes' => array('VISA', 'MASTERCARD', 'DISCOVER'),
                'message' => 'The credit card number you entered is invalid.'))
        ),
        'SecurityCode' => array(
            new Length(array('min' => 3, 'max' => 3))
        )
    ));

    $resolver->setDefaults(array(
        'data_class' => null,
        'constraints' => $collectionConstraint
    ));
}

(src)

(Note: Callback constraints are also allowed and have access to the whole form)

[OskarStark]

Interesting, I think this could be a great addition to the docs. Open for a PR against 5.4 branch?

cc @xabbuh

[xabbuh]

I think it would be a good idea to expand the examples around this a bit.

[PrOF-kk]

Here's the 2nd example brought into more modern PHP.

function configureOptions(OptionsResolver $resolver): void {
    $collectionConstraint = new Collection([
            'CardNumber' => [
                    new CardScheme([
                            'schemes' => ['VISA', 'MASTERCARD', 'DISCOVER'],
                            'message' => 'The credit card number you entered is invalid.'
                    ])
            ],
            'SecurityCode' => [
                    new Length(exactly: 3)
            ]
    ]);

    $resolver->setDefaults([
            'data_class' => null,
            'constraints' => $collectionConstraint
    ]);
}

Should I create a complete example formtype or two for this?

[OskarStark]

Friendly ping @alexandre-daubois if you want to help 🤓

[alexandre-daubois]

I gave it a try!