@unique annotation support for Symfony 2 Validator with Nette, for more info see: http://docs.symfony-reloaded.org/guides/validator.html

Unique.php

<?php

namespace Symfony\Component\Validator\Constraints;

class Unique extends \Symfony\Component\Validator\Constraint
{
	public $message = 'Entity with this property %value% already exists'; # 'Symfony.Validator.Unique.message';
}

UniqueValidator.php

<?php

namespace Symfony\Component\Validator\Constraints;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

class UniqueValidator extends ConstraintValidator
{
	public function isValid($value, Constraint $constraint)
	{
		/* @var $context Symfony\Component\Validator\ValidationContext */
		$context = $this->context;
		
		/* @var $entity Models\Entities\Base */
		$entity = $context->getRoot();

		$property = $context->getCurrentProperty();
		$originalEntityData = $this->getEntityManager()->getUnitOfWork()->getOriginalEntityData($entity);
		$originalValue = isset($originalEntityData[$property]) ? $originalEntityData[$property] : NULL;

		if ($originalValue === $value) { // check if attribute was changed
			return TRUE;
		}

		$class = $entity->getReflection()->getName();
		/* @var $repo Models\Repositories\Base */
		$repo = $this->getEntityManager()->getRepository($class);
		$valid = $repo->exists(array($property => $value)) == FALSE;

		if ($valid) {
			return true;
		} else {
			$this->setMessage($constraint->message, array('value' => $value));
			return false;
		}
	}


	/**
	 * @return Doctrine\ORM\EntityManager
	 */
	private function getEntityManager()
	{
		return \Nette\Environment::getEntityManager();
	}
}