add cookbook entry on creating dynamic forms based on services

cookbook/form/dynamic_form_with_services.rst

@@ -0,0 +1,165 @@
+.. index::
+   single: Form; Events
+
+How to Dynamically Generate Forms based on user data
+====================================================
+
+Sometimes you want a form to be generated dynamically based not only on data
+from this form (see :doc:`Dynamic form generation</cookbook/dynamic_form_generation>`)
+but also on something else. For example depending on the user currently using
+the application. If you have a social website where a user can only message
+people who are his friends on the website, then the current user doesn't need to
+be included as a field of your form, but a "choice list" of whom to message
+should only contain users that are the current user's friends.
+
+Creating the form type
+----------------------
+
+Using an event listener, our form could be built like this::
+
+    namespace Acme\WhateverBundle\FormType;
+
+    use Symfony\Component\Form\AbstractType;
+    use Symfony\Component\Form\FormBuilderInterface;
+    use Symfony\Component\Form\FormEvents;
+    use Symfony\Component\Form\FormEvent;
+    use Symfony\Component\Security\Core\SecurityContext;
+    use Symfony\Component\OptionsResolver\OptionsResolverInterface;
+    use Acme\WhateverBundle\FormSubscriber\UserListener;
+
+    class FriendMessageFormType extends AbstractType
+    {
+        public function buildForm(FormBuilderInterface $builder, array $options)
+        {
+            $builder
+                ->add('subject', 'text')
+                ->add('body', 'textarea')
+            ;
+            $builder->addEventListener(FormEvents::PRE_SET_DATA, function(FormEvent $event){
+                // ... add a choice list of friends of the current application user
+            });
+        }
+
+        public function getName()
+        {
+            return 'acme_friend_message';
+        }
+
+        public function setDefaultOptions(OptionsResolverInterface $resolver)
+        {
+        }
+    }
+
+The problem is now to get the current application user and create a choice field
+that would contain only this user's friends.
+
+Luckily it is pretty easy to inject a service inside of the form. This can be
+done in the constructor.
+
+.. code-block:: php
+
+    private $security_context;
+
+    public function __construct(SecurityContext $security_context)
+    {
+        $this->security_context = $security_context;
+    }
+
+.. note::
+
+    You might wonder, now that we have access to the User (through) the security
+    context, why don't we just use that inside of the buildForm function and
+    still use a listener?
+    This is because doing so in the buildForm method would result in the whole
+    form type being modified and not only one form instance.
+
+Customizing the form type
+-------------------------
+
+Now that we have all the basics in place, we can put everything in place and add
+our listener::
+
+    class FriendMessageFormType extends AbstractType
+    {
+        private $security_context;
+
+        public function __construct(SecurityContext $security_context)
+        {
+            $this->security_context = $security_context;
+        }
+
+        public function buildForm(FormBuilderInterface $builder, array $options)
+        {
+            $builder
+                ->add('subject', 'text')
+                ->add('body', 'textarea')
+            ;
+            $user = $this->security_context->getToken()->getUser();
+            $factory = $builder->getFormFactory();
+
+            $builder->addEventListener(
+                FormEvents::PRE_SET_DATA,
+                function(FormEvent $event) use($user, $factory){
+                    $form = $event->getForm();
+                    $user_id = $user->getId();
+
+                    $form_options = [
+                        'class' => 'Acme\WhateverBundle\Document\User',
+                        'multiple' => false,
+                        'expanded' => false,
+                        'property' => 'fullName',
+                        'query_builder' => function(DocumentRepository $dr) use ($user_id) {
+                            return $dr->createQueryBuilder()->field('friends.$id')->equals(new \MongoId($user_id));
+                        }
+                    ];
+
+                    $form->add($factory->createNamed('friend', 'document', null, $form_options));
+                }
+            );
+        }
+
+        public function getName()
+        {
+            return 'acme_friend_message';
+        }
+
+        public function setDefaultOptions(OptionsResolverInterface $resolver)
+        {
+        }
+    }
+
+Using the form
+--------------
+
+Our form is now ready to use. We have two possible ways to use it inside of a
+controller. Either by creating it everytime and remembering to pass the security
+context, or by defining it as a service. This is the option we will show here.
+
+To define your form as a service, you simply add the configuration to your
+``config.yml`` file.
+
+.. code-block:: yaml
+
+    acme.form.friend_message:
+        class: Acme\WhateverBundle\FormType\FriendMessageType
+        arguments: [@security.context]
+        tags:
+            - { name: form.type, alias: acme_friend_message}
+
+By adding the form as a service, we make sure that this form can now be used
+simply from anywhere. If you need to add it to another form, you will just need
+to use::
+
+    $builder->add('message', 'acme_friend_message');
+
+If you wish to create it from within a controller or any other service that has
+access to the form factory, you then use::
+
+    // src/AcmeDemoBundle/Controller/FriendMessageController.php
+    public function friendMessageAction()
+    {
+        $form = $this->get('form.factory')->create('acme_friend_message');
+        $form = $form->createView();
+
+        return compact('form');
+    }