The purpose of the Callback constraint is to create completely custom validation rules and to assign any validation errors to specific fields on your object. If you're using validation with forms, this means that you can make these custom errors display next to a specific field, instead of simply at the top of your form.
This process works by specifying one or more callback methods, each of which will be called during the validation process. Each of those methods can do anything, including creating and assigning validation errors.
Note
A callback method itself doesn't fail or return any value. Instead, as you'll see in the example, a callback method has the ability to directly add validator "violations".
.. configuration-block::
.. code-block:: php-annotations
// src/AppBundle/Entity/Author.php
namespace AppBundle\Entity;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;
// if you're using the older 2.4 validation API, you'll need this instead
// use Symfony\Component\Validator\ExecutionContextInterface;
class Author
{
/**
* @Assert\Callback
*/
public function validate(ExecutionContextInterface $context)
{
// ...
}
}
.. code-block:: yaml
# src/AppBundle/Resources/config/validation.yml
AppBundle\Entity\Author:
constraints:
- Callback: validate
.. code-block:: xml
<!-- src/AppBundle/Resources/config/validation.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
<class name="AppBundle\Entity\Author">
<constraint name="Callback">validate</constraint>
</class>
</constraint-mapping>
.. code-block:: php
// src/AppBundle/Entity/Author.php
namespace AppBundle\Entity;
use Symfony\Component\Validator\Mapping\ClassMetadata;
use Symfony\Component\Validator\Constraints as Assert;
class Author
{
public static function loadValidatorMetadata(ClassMetadata $metadata)
{
$metadata->addConstraint(new Assert\Callback('validate'));
}
}
The callback method is passed a special ExecutionContextInterface object.
You can set "violations" directly on this object and determine to which
field those errors should be attributed:
// ...
use Symfony\Component\Validator\Context\ExecutionContextInterface;
// if you're using the older 2.4 validation API, you'll need this instead
// use Symfony\Component\Validator\ExecutionContextInterface;
class Author
{
// ...
private $firstName;
public function validate(ExecutionContextInterface $context)
{
// somehow you have an array of "fake names"
$fakeNames = array(/* ... */);
// check if the name is actually a fake name
if (in_array($this->getFirstName(), $fakeNames)) {
// If you're using the new 2.5 validation API (you probably are!)
$context->buildViolation('This name sounds totally fake!')
->atPath('firstName')
->addViolation();
// If you're using the old 2.4 validation API
/*
$context->addViolationAt(
'firstName',
'This name sounds totally fake!'
);
*/
}
}
}
You can also use the constraint with static methods. Since static methods don't have access to the object instance, they receive the object as the first argument:
public static function validate($object, ExecutionContextInterface $context)
{
// somehow you have an array of "fake names"
$fakeNames = array(/* ... */);
// check if the name is actually a fake name
if (in_array($object->getFirstName(), $fakeNames)) {
// If you're using the new 2.5 validation API (you probably are!)
$context->buildViolation('This name sounds totally fake!')
->atPath('firstName')
->addViolation()
;
// If you're using the old 2.4 validation API
/*
$context->addViolationAt(
'firstName',
'This name sounds totally fake!'
);
*/
}
}
If you want to execute a static callback method that is not located in the
class of the validated object, you can configure the constraint to invoke
an array callable as supported by PHP's :phpfunction:`call_user_func` function.
Suppose your validation function is Acme\Validator::validate():
namespace Acme;
use Symfony\Component\Validator\Context\ExecutionContextInterface;
// if you're using the older 2.4 validation API, you'll need this instead
// use Symfony\Component\Validator\ExecutionContextInterface;
class Validator
{
public static function validate($object, ExecutionContextInterface $context)
{
// ...
}
}
You can then use the following configuration to invoke this validator:
.. configuration-block::
.. code-block:: php-annotations
// src/AppBundle/Entity/Author.php
namespace AppBundle\Entity;
use Symfony\Component\Validator\Constraints as Assert;
/**
* @Assert\Callback({"Acme\Validator", "validate"})
*/
class Author
{
}
.. code-block:: yaml
# src/AppBundle/Resources/config/validation.yml
AppBundle\Entity\Author:
constraints:
- Callback: [Acme\Validator, validate]
.. code-block:: xml
<!-- src/AppBundle/Resources/config/validation.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
<class name="AppBundle\Entity\Author">
<constraint name="Callback">
<value>Acme\Validator</value>
<value>validate</value>
</constraint>
</class>
</constraint-mapping>
.. code-block:: php
// src/AppBundle/Entity/Author.php
namespace AppBundle\Entity;
use Acme\Validator;
use Symfony\Component\Validator\Mapping\ClassMetadata;
use Symfony\Component\Validator\Constraints as Assert;
class Author
{
public static function loadValidatorMetadata(ClassMetadata $metadata)
{
$metadata->addConstraint(new Assert\Callback(array(
Validator::class,
'validate',
)));
}
}
Note
The Callback constraint does not support global callback functions nor is it possible to specify a global function or a service method as callback. To validate using a service, you should :doc:`create a custom validation constraint </validation/custom_constraint>` and add that new constraint to your class.
When configuring the constraint via PHP, you can also pass a closure to the constructor of the Callback constraint:
// src/AppBundle/Entity/Author.php
namespace AppBundle\Entity;
use Symfony\Component\Validator\Context\ExecutionContextInterface;
// if you're using the older 2.4 validation API, you'll need this instead
// use Symfony\Component\Validator\ExecutionContextInterface;
use Symfony\Component\Validator\Mapping\ClassMetadata;
use Symfony\Component\Validator\Constraints as Assert;
class Author
{
public static function loadValidatorMetadata(ClassMetadata $metadata)
{
$callback = function ($object, ExecutionContextInterface $context) {
// ...
};
$metadata->addConstraint(new Assert\Callback($callback));
}
}
type: string, array or Closure [:ref:`default option <validation-default-option>`]
The callback option accepts three different formats for specifying the callback method:
- A string containing the name of a concrete or static method;
- An array callable with the format
array('<Class>', '<method>'); - A closure.
Concrete callbacks receive an :class:`Symfony\\Component\\Validator\\Context\\ExecutionContextInterface` instance as only argument.
Static or closure callbacks receive the validated object as the first argument and the :class:`Symfony\\Component\\Validator\\ExecutionContextInterface` instance as the second argument.