表单：避免将非提交字段设置为 null

我有一个简单的模型（源简化）：

class Collection
{
    public $page;
    public $limit;
}

以及表单类型：

class CollectionType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('page', 'integer');
        $builder->add('limit', 'integer');
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'FSC\Common\Rest\Form\Model\Collection',
        ));
    }
}

我的控制器：

public function getUsersAction(Request $request)
{
    $collection = new Collection();
    $collection->page = 1;
    $collection->limit = 10;

    $form = $this->createForm(new CollectionType(), $collection)
    $form->bind($request);

    print_r($collection);exit;
}

When i POST /users/?form[page]=2&form[limit]=20，响应是我所期望的：

Collection Object
(
    [page:public] => 2
    [limit:public] => 20
)

现在，当我POST /users/?form[page]=3，响应为：

Collection Object
(
    [page:public] => 3
    [limit:public] =>
)

limit变为 null，因为未提交。

我想得到

Collection Object
(
    [page:public] => 3
    [limit:public] => 10 // The default value, set before the bind
)

Question：我如何更改表单行为，以便它忽略未提交的值？

如果只是参数（GET参数）的问题，您可以在路由文件中定义默认值

route_name:
pattern: /users/?form[page]={page}&form[limit]={limit}
defaults: { _controller: CompanyNameBundleName:ControllerName:ActionName, 
                         limit:10 }

另一种方法可能是使用hook (i.e. PRE_BIND https://github.com/symfony/Form/blob/master/FormEvents.php）并手动将该值更新到此事件中。这样你就没有将“逻辑”传播到多段代码中。

最终代码 - 由 Adrien 建议 - 将是

<?php

use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormFactoryInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Form\FormEvents;

class IgnoreNonSubmittedFieldSubscriber implements EventSubscriberInterface
{
    private $factory;

    public function __construct(FormFactoryInterface $factory)
    {
        $this->factory = $factory;
    }

    public static function getSubscribedEvents()
    {
        return array(FormEvents::PRE_BIND => 'preBind');
    }

    public function preBind(FormEvent $event)
    {
        $submittedData = $event->getData();
        $form = $event->getForm();

        // We remove every child that has no data to bind, to avoid "overriding" the form default data
        foreach ($form->all() as $name => $child) {
            if (!isset($submittedData[$name])) {
                $form->remove($name);
            }
        }
    }
}