Forms

• Define a FormType class describing each field, its options, constraints, and validation.
• `$form->handleRequest($request)` populates the bound model from POST/PUT data.
• `$form->isSubmitted() && $form->isValid()` is the canonical guard before persisting.
• Data transformers convert between view (string) and model (object/scalar) representations.
• Form events (`PRE_SET_DATA`, `PRE_SUBMIT`, `POST_SUBMIT`) let you build dynamic forms (dependent dropdowns).
• Render with Twig's form helpers: `form_start`, `form_widget`, `form_row`, `form_end`.

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $b, array $options): void
    {
        $b->add('email', EmailType::class, ['constraints' => [new Email(), new NotBlank()]]);
    }

    public function configureOptions(OptionsResolver $r): void
    {
        $r->setDefaults(['data_class' => User::class]);
    }
}