Form Field Guessing¶

Remember when we disabled HTML5 validation earlier. Let’s add it back temporarily. Remove the novalidate attribute so that it works again:

{# src/Yoda/UserBundle/Resources/views/Register/register.html.twig #}

{# ... #}
<form action="{{ path('user_register') }}" method="POST">

Now, open the User class: let’s do a little experimenting. Let’s pretend that the email field isn’t requied. Remove the NotBlank constraint from it and set a nullable=true option in the Doctrine metadata. Don’t worry about updating your schema - this change is just temporary:

// src/Yoda/UserBundle/Entity/User.php
// ...

/**
 * @ORM\Column(type="string", length=255, nullable=true)
 * @Assert\Email
 */
private $email;

Now, open up RegisterFormType and remove the required option, which determines whether or not the HTML5 required attribute should be rendered:

// src/Yoda/UserBundle/Form/RegisterFormType.php
// ...

$builder
    // ...
    ->add('email', 'email', array(
        'label' => 'Email Address',
        'attr'    => array('class' => 'C-3PO')
    ))
    // ...
;

When we surf to the registration page and try to submit, HTML5 validation stops us. And just like before, the email field has the required attribute on it. We saw earlier that we can fix the problem by setting the required option to false for that field. But shouldn’t the form be able to see that the email field isn’t required in User and set the option to false for us?

Actually, it can! The feature is called “field guessing” and it works like this. Set the second argument of add for the email field to null:

// src/Yoda/UserBundle/Form/RegisterFormType.php
// ...

$builder
    // ...
    ->add('email', null, array(
        'required' => false,
        'label' => 'Email Address',
        'attr'    => array('class' => 'C-3PO')
    ))
    // ...
;

This might seem a little crazy, because this argument normally tells Symfony what type of field this is. Will it be able to figure how to render this field?

Refresh the page and inspect email - there are a bunch of awesome things happening:

<input type="email" id="user_register_email" name="user_register[email]" maxlength="255" />

First, notice that the field is still type="email". That’s being guessed based on the fact that there is an Email constraint on the property. Remove the Email constraint and refresh:

// src/Yoda/UserBundle/Entity/User.php
// ...

/**
 * @ORM\Column(type="string", length=255, nullable=true)
 */
private $email;

<input type="text" id="user_register_email" name="user_register[email]" maxlength="255" />

Symfony doesn’t know anything about the field now, so it just defaults to the text type.

Field Option Guessing¶

But now, notice that the required attribute is gone. In addition to guessing the field type, certain options are also guessed, like the required option. Let’s play with this. Add back the NotBlank constraint and refresh:

/**
 * @ORM\Column(type="string", length=255, nullable=true)
 * @Assert\NotBlank()
 */
private $email;

Not surprisingly, the required attribute is back. Next, remove NotBlank, but also make the field not null:

/**
 * @ORM\Column(type="string", length=255, nullable=false)
 */
private $email;

Yep, the required attribute is still there. The form system guesses that the field is required based on the fact that it’s required in the database.

Even the maxlength attribute that’s being rendered comes from the length of the field in the database.

So here’s the deal. If you leave the second argument empty when creating a field, Symfony will try to guess the field type and some options, like required, max_length and pattern. Field guessing isn’t always perfect, but I tend to try it at first and explicitly set things that aren’t guessed correctly.

Let’s put our 2 validation constraints back and add back the email type option in the form and refresh:

// src/Yoda/UserBundle/Entity/User.php
/**
 * @ORM\Column(type="string", length=255)
 * @Assert\NotBlank
 * @Assert\Email
 */
private $email;

// src/Yoda/UserBundle/Form/RegisterFormType.php

$builder
    // ...
    ->add('email', 'email')
    // ...
;

If you were watching closely, the maxlength attribute disappeared:

<input type="text" id="user_register_email" name="user_register[email]" required="required" />

This is a gotcha with guessing. As soon as you pass in the type argument, none of the options like required or max_length are guessed anymore. In other words, if you don’t let Symfony guess the field type, it won’t guess any of the options either.