How to Create a Custom Validation Constraint
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How to Create a Custom Validation Constraint
You can create a custom constraint by extending the base constraint class, Constraint. As an example you're going to create a basic validator that checks if a string contains only alphanumeric characters.
Creating the Constraint Class
First you need to create a Constraint class and extend Constraint:
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// src/Validator/ContainsAlphanumeric.php
namespace App\Validator;
use Symfony\Component\Validator\Constraint;
#[\Attribute]
class ContainsAlphanumeric extends Constraint
{
public string $message = 'The string "{{ string }}" contains an illegal character: it can only contain letters or numbers.';
// If the constraint has configuration options, define them as public properties
public string $mode = 'strict';
}
Add #[\Attribute]
to the constraint class if you want to
use it as an attribute in other classes.
6.1
The #[HasNamedArguments]
attribute was introduced in Symfony 6.1.
You can use #[HasNamedArguments]
to make some constraint options required:
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// src/Validator/ContainsAlphanumeric.php
namespace App\Validator;
use Symfony\Component\Validator\Attribute\HasNamedArguments;
use Symfony\Component\Validator\Constraint;
#[\Attribute]
class ContainsAlphanumeric extends Constraint
{
public $message = 'The string "{{ string }}" contains an illegal character: it can only contain letters or numbers.';
public string $mode;
#[HasNamedArguments]
public function __construct(string $mode, array $groups = null, mixed $payload = null)
{
parent::__construct([], $groups, $payload);
$this->mode = $mode;
}
}
Creating the Validator itself
As you can see, a constraint class is fairly minimal. The actual validation is
performed by another "constraint validator" class. The constraint validator
class is specified by the constraint's validatedBy()
method, which
has this default logic:
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// in the base Symfony\Component\Validator\Constraint class
public function validatedBy()
{
return static::class.'Validator';
}
In other words, if you create a custom Constraint
(e.g. MyConstraint
),
Symfony will automatically look for another class, MyConstraintValidator
when actually performing the validation.
The validator class only has one required method validate()
:
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// src/Validator/ContainsAlphanumericValidator.php
namespace App\Validator;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Exception\UnexpectedTypeException;
use Symfony\Component\Validator\Exception\UnexpectedValueException;
class ContainsAlphanumericValidator extends ConstraintValidator
{
public function validate($value, Constraint $constraint): void
{
if (!$constraint instanceof ContainsAlphanumeric) {
throw new UnexpectedTypeException($constraint, ContainsAlphanumeric::class);
}
// custom constraints should ignore null and empty values to allow
// other constraints (NotBlank, NotNull, etc.) to take care of that
if (null === $value || '' === $value) {
return;
}
if (!is_string($value)) {
// throw this exception if your validator cannot handle the passed type so that it can be marked as invalid
throw new UnexpectedValueException($value, 'string');
// separate multiple types using pipes
// throw new UnexpectedValueException($value, 'string|int');
}
// access your configuration options like this:
if ('strict' === $constraint->mode) {
// ...
}
if (!preg_match('/^[a-zA-Z0-9]+$/', $value, $matches)) {
// the argument must be a string or an object implementing __toString()
$this->context->buildViolation($constraint->message)
->setParameter('{{ string }}', $value)
->addViolation();
}
}
}
Inside validate()
, you don't need to return a value. Instead, you add violations
to the validator's context
property and a value will be considered valid
if it causes no violations. The buildViolation()
method takes the error
message as its argument and returns an instance of
ConstraintViolationBuilderInterface.
The addViolation()
method call finally adds the violation to the context.
Using the new Validator
You can use custom validators like the ones provided by Symfony itself:
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// src/Entity/AcmeEntity.php
namespace App\Entity;
use App\Validator as AcmeAssert;
use Symfony\Component\Validator\Constraints as Assert;
class AcmeEntity
{
// ...
#[Assert\NotBlank]
#[AcmeAssert\ContainsAlphanumeric(mode: 'loose')]
protected string $name;
// ...
}
If your constraint contains options, then they should be public properties on the custom Constraint class you created earlier. These options can be configured like options on core Symfony constraints.
Constraint Validators with Dependencies
If you're using the default services.yaml configuration,
then your validator is already registered as a service and tagged
with the necessary validator.constraint_validator
. This means you can
inject services or configuration like any other service.
Create a Reusable Set of Constraints
In case you need to consistently apply a common set of constraints across your application, you can extend the Compound constraint.
Class Constraint Validator
Besides validating a single property, a constraint can have an entire class as its scope.
For instance, imagine you also have a PaymentReceipt
entity and you
need to make sure the email of the receipt payload matches the user's
email. First, create a constraint and override the getTargets()
method:
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// src/Validator/ConfirmedPaymentReceipt.php
namespace App\Validator;
use Symfony\Component\Validator\Constraint;
#[\Attribute]
class ConfirmedPaymentReceipt extends Constraint
{
public string $userDoesNotMatchMessage = 'User\'s e-mail address does not match that of the receipt';
public function getTargets(): string
{
return self::CLASS_CONSTRAINT;
}
}
Now, the constraint validator will get an object as the first argument to
validate()
:
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// src/Validator/ConfirmedPaymentReceiptValidator.php
namespace App\Validator;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Exception\UnexpectedValueException;
class ConfirmedPaymentReceiptValidator extends ConstraintValidator
{
/**
* @param PaymentReceipt $receipt
*/
public function validate($receipt, Constraint $constraint): void
{
if (!$receipt instanceof PaymentReceipt) {
throw new UnexpectedValueException($receipt, PaymentReceipt::class);
}
if (!$constraint instanceof ConfirmedPaymentReceipt) {
throw new UnexpectedValueException($constraint, ConfirmedPaymentReceipt::class);
}
$receiptEmail = $receipt->getPayload()['email'] ?? null;
$userEmail = $receipt->getUser()->getEmail();
if ($userEmail !== $receiptEmail) {
$this->context
->buildViolation($constraint->userDoesNotMatchMessage)
->atPath('user.email')
->addViolation();
}
}
}
Tip
The atPath()
method defines the property with which the validation error is
associated. Use any valid PropertyAccess syntax
to define that property.
A class constraint validator must be applied to the class itself:
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// src/Entity/AcmeEntity.php
namespace App\Entity;
use App\Validator as AcmeAssert;
#[AcmeAssert\ProtocolClass]
class AcmeEntity
{
// ...
}
Testing Custom Constraints
Use the ConstraintValidatorTestCase` class to simplify writing unit tests for your custom constraints:
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// tests/Validator/ContainsAlphanumericValidatorTest.php
namespace App\Tests\Validator;
use App\Validator\ContainsAlphanumeric;
use App\Validator\ContainsAlphanumericValidator;
use Symfony\Component\Validator\Test\ConstraintValidatorTestCase;
class ContainsAlphanumericValidatorTest extends ConstraintValidatorTestCase
{
protected function createValidator()
{
return new ContainsAlphanumericValidator();
}
public function testNullIsValid()
{
$this->validator->validate(null, new ContainsAlphanumeric());
$this->assertNoViolation();
}
/**
* @dataProvider provideInvalidConstraints
*/
public function testTrueIsInvalid(ContainsAlphanumeric $constraint)
{
$this->validator->validate('...', $constraint);
$this->buildViolation('myMessage')
->setParameter('{{ string }}', '...')
->assertRaised();
}
public function provideInvalidConstraints(): iterable
{
yield [new ContainsAlphanumeric(message: 'myMessage')];
// ...
}
}