Use UniqueEntity outside of entity and without forms - symfony

Question

I need to validate an email passed by user:
private function validate($value): bool
{
$violations = $this->validator->validate($value, [
new Assert\NotBlank(),
new Assert\Email(),
new UniqueEntity([
'entityClass' => User::class,
'fields' => 'email',
])
]);
return count($violations) === 0;
}
But UniqueEntity constraint throws an exception:
Warning: get_class() expects parameter 1 to be object, string given
Seems like ValidatorInterface::validate() method's first argument awaiting for Entity object with getEmail() method, but it looks ugly.
Is there any elegant way to validate uniqueness of field passing only scalar value to ValidatorInterface::validate() method?

Answer 1

Seems like there is no built-in Symfony solution to do what I want, so I created custom constraint as Jakub Matczak suggested.
UPD: This solution throws a validation error when you're sending form to edit your entity. To avoid this behavior you'll need to improve this constraint manually.
Constraint:
namespace AppBundle\Validator\Constraints;
use Symfony\Component\Validator\Constraint;
class UniqueValueInEntity extends Constraint
{
public $message = 'This value is already used.';
public $entityClass;
public $field;
public function getRequiredOptions()
{
return ['entityClass', 'field'];
}
public function getTargets()
{
return self::PROPERTY_CONSTRAINT;
}
public function validatedBy()
{
return get_class($this).'Validator';
}
}
Validator:
namespace AppBundle\Validator\Constraints;
use Doctrine\ORM\EntityManager;
use InvalidArgumentException;
use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
class UniqueValueInEntityValidator extends ConstraintValidator
{
/**
* #var EntityManager
*/
private $em;
public function __construct(EntityManager $em)
{
$this->em = $em;
}
public function validate($value, Constraint $constraint)
{
$entityRepository = $this->em->getRepository($constraint->entityClass);
if (!is_scalar($constraint->field)) {
throw new InvalidArgumentException('"field" parameter should be any scalar type');
}
$searchResults = $entityRepository->findBy([
$constraint->field => $value
]);
if (count($searchResults) > 0) {
$this->context->buildViolation($constraint->message)
->addViolation();
}
}
}
Service:
services:
app.validator.unique_value_in_entity:
class: AppBundle\Validator\Constraints\UniqueValueInEntityValidator
arguments: ['#doctrine.orm.entity_manager']
tags:
- { name: validator.constraint_validator }
Usage example:
private function validate($value): bool
{
$violations = $this->validator->validate($value, [
new Assert\NotBlank(),
new Assert\Email(),
new UniqueValueInEntity([
'entityClass' => User::class,
'field' => 'email',
])
]);
return count($violations) === 0;
}

Answer 2

For this porpose i would use #UniqueEntity(fields={"email"}) in user class annotation. Kind of this way:
/**
* #ORM\Entity()
* #ORM\Table(name="user")
* #UniqueEntity(fields={"email"})
*/