The virtual form field option can be very useful when you have some duplicated fields in different entities.

当您在不同的实体中拥有一些重复的表单域时，虚拟表单域选项就显得非常有用。

For example, imagine you have two entities, a Company and a Customer:

举个例子，想象您有两个实体，Company和Customer：

Company实体：

1. // src/Acme/HelloBundle/Entity/Company.php 
2. namespace Acme\HelloBundle\Entity; 
3.  
4. class Company 
5. { 
6.     private $name; 
7.     private $website; 
8.  
9.     private $address; 
10.     private $zipcode; 
11.     private $city; 
12.     private $country; 
13. } 

 Customer实体：

1. // src/Acme/HelloBundle/Entity/Customer.php 
2. namespace Acme\HelloBundle\Entity; 
3.  
4. class Customer 
5. { 
6.     private $firstName; 
7.     private $lastName; 
8.  
9.     private $address; 
10.     private $zipcode; 
11.     private $city; 
12.     private $country; 
13. } 

Like you can see, each entity shares a few of the same fields: address, zipcode, city, country.

正如您所见，每个实体都有着一些相同的表单域：address、zipcode、city和country。

Now, you want to build two forms: one for a Company and the second for a Customer.

现在，您要创建两个表单：一个对应Company，第二个对应Customer。

Start by creating a very simple CompanyType and CustomerType:

首先创建一个非常简单的CompanyType和CustomerType：

CompanyType类：

1. // src/Acme/HelloBundle/Form/Type/CompanyType.php 
2. namespace Acme\HelloBundle\Form\Type; 
3.  
4. use Symfony\Component\Form\FormBuilderInterface; 
5.  
6. class CompanyType extends AbstractType 
7. { 
8.     public function buildForm(FormBuilderInterface $builder, array $options) 
9.     { 
10.         $builder 
11.             ->add('name', 'text') 
12.             ->add('website', 'text'); 
13.     } 
14. } 

 CustomerType类：

1. // src/Acme/HelloBundle/Form/Type/CustomerType.php 
2. namespace Acme\HelloBundle\Form\Type; 
3.  
4. use Symfony\Component\Form\FormBuilderInterface; 
5.  
6. class CustomerType extends AbstractType 
7. { 
8.     public function buildForm(FormBuilderInterface $builder, array $options) 
9.     { 
10.         $builder 
11.             ->add('firstName', 'text') 
12.             ->add('lastName', 'text'); 
13.     } 
14. } 

Now, we have to deal with the four duplicated fields. Here is a (simple) location form type:

现在我们需要处理那四个重复的表单域。下面是个（简单）的位置表单类型：

1. // src/Acme/HelloBundle/Form/Type/LocationType.php 
2. namespace Acme\HelloBundle\Form\Type; 
3.  
4. use Symfony\Component\Form\FormBuilderInterface; 
5. use Symfony\Component\OptionsResolver\OptionsResolverInterface; 
6.  
7. class LocationType extends AbstractType 
8. { 
9.     public function buildForm(FormBuilderInterface $builder, array $options) 
10.     { 
11.         $builder 
12.             ->add('address', 'textarea') 
13.             ->add('zipcode', 'text') 
14.             ->add('city', 'text') 
15.             ->add('country', 'text'); 
16.     } 
17.  
18.     public function setDefaultOptions(OptionsResolverInterface $resolver) 
19.     { 
20.         $resolver->setDefaults(array( 
21.             'virtual' => true 
22.         )); 
23.     } 
24.  
25.     public function getName() 
26.     { 
27.         return 'location'; 
28.     } 
29. } 

We don't actually have a location field in each of our entities, so we can't directly link our LocationType to our CompanyType or CustomerType. But we absolutely want to have a dedicated form type to deal with location (remember, DRY!).

实际上在每个实体中我们并没有location表单域，因此我们不能直接将LocationType链入我们的CompanyType或CustomerType中。但我们又绝对想要一个专门处理位置的表单类型（记住，DRY！）

The virtual form field option is the solution.

解决这个问题就需要用到虚拟表单域选项了。

We can set the option 'virtual' => true in the setDefaultOptions() method of LocationType and directly start using it in the two original form types.

我们可以在LocationType类中的setDefaultOptions()方法中将选项'virtual'设置为true，并且在两个原始域类型中直接使用它。

Look at the result:

所下所示：

CompanyType类：

1. // CompanyType 
2. public function buildForm(FormBuilderInterface $builder, array $options) 
3. { 
4.     $builder->add('foo', new LocationType(), array( 
5.         'data_class' => 'Acme\HelloBundle\Entity\Company' 
6.     )); 
7. } 

 CustomerType类：

1. // CustomerType 
2. public function buildForm(FormBuilderInterface $builder, array $options) 
3. { 
4.     $builder->add('bar', new LocationType(), array( 
5.         'data_class' => 'Acme\HelloBundle\Entity\Customer' 
6.     )); 
7. } 

With the virtual option set to false (default behavior), the Form Component expects each underlying object to have a foo (or bar) property that is either some object or array which contains the four location fields. Of course, we don't have this object/array in our entities and we don't want it!

当virtual选项设为false时（缺省值），表单组件期望每个相关的对象都有一个foo（或bar）属性，要么是一些对象，要么是包含四个位置表单域的数组。当然，在我们的实体中没有这样的对象或数组，而且我们也不想那样做！

With the virtual option set to true, the Form component skips the foo (or bar) property, and instead "gets" and "sets" the 4 location fields directly on the underlying object!

当virtual选项设为true时，表单组件忽略foo（或bar）属性，取而代之的是在相关对象中直接"gets"和"sets"这4个位置表单域！

Instead of setting the virtual option inside LocationType, you can (just like with any options) also pass it in as an array option to the third argument of $builder->add(). 如果不使用在LocationType中设置virtual选项，您也可以（如其它选项那样）将其作为一个数组选项发送到$builder->add()的第三个参数。

本文转自 firehare 51CTO博客，原文链接：http://blog.51cto.com/firehare/1004587，如需转载请自行联系原作者