UPGRADE FROM 2.5 to 2.6

Known Backwards-Compatibility Breaks

If you use the PdoSessionHandler, the session table now has a different schema and must be modified. Look below for more details.

Form

The "empty_value" option in the types "choice", "date", "datetime" and "time" was deprecated and replaced by a new option "placeholder". You should use the option "placeholder" together with the view variables "placeholder" and "placeholder_in_choices" now.

The option "empty_value" and the view variables "empty_value" and "empty_value_in_choices" will be removed in Symfony 3.0.

Before:

$form->add('category', 'choice', array(
    'choices' => array('politics', 'media'),
    'empty_value' => 'Select a category...',
));

After:

$form->add('category', 'choice', array(
    'choices' => array('politics', 'media'),
    'placeholder' => 'Select a category...',
));

Before:

{{ form.vars.empty_value }}

{% if form.vars.empty_value_in_choices %}
    ...
{% endif %}

After:

{{ form.vars.placeholder }}

{% if form.vars.placeholder_in_choices %}
    ...
{% endif %}

Validator

The internal method setConstraint() was added to Symfony\Component\Validator\Context\ExecutionContextInterface. With this method, the context is informed about the constraint that is currently being validated.

If you implement this interface, make sure to add the method to your implementation. The easiest solution is to just implement an empty method:
```
public function setConstraint(Constraint $constraint)
{
}
```
Prior to 2.6 Symfony\Component\Validator\Constraints\ExpressionValidator would not execute the Expression if it was attached to a property on an object and that property was set to null or an empty string.

To emulate the old behaviour change your expression to something like this:
```
value == null or (YOUR_EXPRESSION)
```

Security

The SecurityContextInterface is marked as deprecated in favor of the Symfony\Component\Security\Core\Authorization\AuthorizationCheckerInterface and Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorageInterface.
```
isGranted  => AuthorizationCheckerInterface
getToken   => TokenStorageInterface
setToken   => TokenStorageInterface
```
The Implementations have moved too, The SecurityContext is marked as deprecated and has been split to use the AuthorizationCheckerInterface and TokenStorage. This change is 100% Backwards Compatible as the SecurityContext delegates the methods.

The service security.context is deprecated along with the above change. Recommended to use instead:

@security.authorization_checker => isGranted()
@security.token_storage         => getToken()
@security.token_storage         => setToken()

HttpFoundation

The PdoSessionHandler to store sessions in a database changed significantly. This introduced a backwards-compatibility break in the schema of the session table. The following changes must be made to your session table:
- Add a new integer column called sess_lifetime. Assuming you have the default column and table names, in MySQL this would be: ALTER TABLE session ADD sess_lifetime INT NOT NULL ;
- Change the data column (default: sess_value) to be a Blob type. In MySQL this would be: ALTER TABLE session CHANGE sess_value session_value BLOB NOT NULL;
There is also an issue that affects Windows servers.

A legacy class, LegacyPdoSessionHandler has been created to ease backwards-compatibility issues when upgrading.

The changes to the PdoSessionHandler are:
- By default, it now implements session locking to prevent loss of data by concurrent access to the same session.
  - It does so using a transaction between opening and closing a session. For this reason, it's not recommended to use the same database connection that you also use for your application logic. Otherwise you have to make sure to access your database after the session is closed and committed. Instead of passing an existing connection to the handler, you can now also pass a DSN string which will be used to lazy-connect when a session is started.
  - Since accessing a session now blocks when the same session is still open, it is best practice to save the session as soon as you don't need to write to it anymore. For example, read-only AJAX request to a session can save the session immediately after opening it to increase concurrency.
  - As alternative to transactional locking you can also use advisory locks which do not require a transaction. Additionally, you can also revert back to no locking in case you have custom logic to deal with race conditions like an optimistic concurrency control approach. The locking strategy can be chosen by passing the corresponding constant as lock_mode option, e.g. new PdoSessionHandler($pdoOrDsn, array('lock_mode' => PdoSessionHandler::LOCK_NONE)). For more information please read the class documentation.
- The expected schema of the table changed.
  - Session data is binary text that can contain null bytes and thus should also be saved as-is in a binary column like BLOB. For this reason, the handler does not base64_encode the data anymore.
  - A new column to store the lifetime of a session is required. This allows to have different lifetimes per session configured via session.gc_maxlifetime ini setting.
  - You would need to migrate the table manually if you want to keep session information of your users.
  - You could use PdoSessionHandler::createTable to initialize a correctly defined table depending on the used database vendor.

OptionsResolver

The "array" type hint was removed from the OptionsResolverInterface methods setRequired(), setAllowedValues(), addAllowedValues(), setAllowedTypes() and addAllowedTypes(). You must remove the type hint from your implementations.
The interface OptionsResolverInterface was deprecated, since OptionsResolver instances are not supposed to be shared between classes. You should type hint against OptionsResolver instead.

Before:
```
protected function configureOptions(OptionsResolverInterface $resolver)
{
    // ...
}
```
After:
```
protected function configureOptions(OptionsResolver $resolver)
{
    // ...
}
```

OptionsResolver::isRequired() now returns true if a required option has a default value set. The new method isMissing() exhibits the old functionality of isRequired().

Before:

$resolver->setRequired(array('port'));

$resolver->isRequired('port');
// => true

$resolver->setDefaults(array('port' => 25));

$resolver->isRequired('port');
// => false

After:

$resolver->setRequired(array('port'));

$resolver->isRequired('port');
// => true
$resolver->isMissing('port');
// => true

$resolver->setDefaults(array('port' => 25));

$resolver->isRequired('port');
// => true
$resolver->isMissing('port');
// => false

OptionsResolver::replaceDefaults() was deprecated. Use clear() and setDefaults() instead.

Before:

$resolver->replaceDefaults(array(
    'port' => 25,
));

After:

$resolver->clear();
$resolver->setDefaults(array(
    'port' => 25,
));

OptionsResolver::setOptional() was deprecated. Use setDefined() instead.

Before:
```
$resolver->setOptional(array('port'));
```
After:
```
$resolver->setDefined('port');
```

OptionsResolver::isKnown() was deprecated. Use isDefined() instead.

Before:

if ($resolver->isKnown('port')) {
    // ...
}

After:

if ($resolver->isDefined('port')) {
    // ...
}

The methods setAllowedValues(), addAllowedValues(), setAllowedTypes() and addAllowedTypes() were changed to modify one option at a time instead of batch processing options. The old API exists for backwards compatibility, but will be removed in Symfony 3.0.

Before:
```
$resolver->setAllowedValues(array(
    'method' => array('POST', 'GET'),
));
```
After:
```
$resolver->setAllowedValues('method', array('POST', 'GET'));
```
The class Options was merged into OptionsResolver. If you instantiated this class manually, you should instantiate OptionsResolver now. Options is now a marker interface implemented by OptionsResolver.

Before:
```
$options = new Options();
```
After:
```
$resolver = new OptionsResolver();
```

Normalizers for defined but unset options are not executed anymore. If you want to have them executed, you should define a default value.

Before:

$resolver->setOptional(array('port'));
$resolver->setNormalizers(array(
    'port' => function ($options, $value) {
        // return normalized value
    }
));

$options = $resolver->resolve($options);

After:

$resolver->setDefault('port', null);
$resolver->setNormalizer('port', function ($options, $value) {
    // return normalized value
});

$options = $resolver->resolve($options);

When undefined options are passed, resolve() now throws an UndefinedOptionsException instead of an InvalidOptionsException. InvalidOptionsException is only thrown when option values fail their validation constraints.

Before:

$resolver->setDefaults(array(
    'transport' => 'smtp',
    'port' => 25,
));
$resolver->setAllowedTypes(array(
    'port' => 'integer',
));

// throws InvalidOptionsException
$resolver->resolve(array('foo' => 'bar'));

// throws InvalidOptionsException
$resolver->resolve(array('port' => '25'));

After:

$resolver->setDefaults(array(
    'transport' => 'smtp',
    'port' => 25,
));
$resolver->setAllowedTypes(array(
    'port' => 'integer',
));

// throws UndefinedOptionsException
$resolver->resolve(array('foo' => 'bar'));

// throws InvalidOptionsException
$resolver->resolve(array('port' => '25'));

VarDumper and DebugBundle

The component and the bundle are new to Symfony 2.6. We encourage you to enable the bundle in your app/AppKernel.php for the dev or test environments. Just add this line before loading the WebProfilerBundle:

$bundles[] = new Symfony\Bundle\DebugBundle\DebugBundle();

Then enjoy dumping variables by calling dump($var) anywhere in your PHP and {% dump var %} or {{ dump(var) }} in Twig. Dumps are displayed in the web debug toolbar.

Translation

With LoggingTranslator, a new translator class is introduced with Symfony 2.6. By default, the @translator service is referring to this class in the debug environment.

If you have your own services that depend on the @translator service and expect this service to be an instance of either Symfony\Component\Translation\Translator or Symfony\Bundle\FrameworkBundle\Translation\Translator, e.g. by type-hinting for either of these classes, you will need to change that type hint. You can use the TranslatorInterface to be on the safe side for future changes.

Before:

use Symfony\Component\Translation\Translator;

class MyService {
    public function __construct(Translator $translator)
    {
        ...
    }
}

After:

use Symfony\Component\Translation\TranslatorInterface;

class MyService {
    public function __construct(TranslatorInterface $translator)
    {
        ...
    }
}

Uh oh!