Example Doctrine 2 uniqueness validator for Zend_Form or such

gistfile1.aw

<?php
use Doctrine\ORM\EntityRepository;

class Wantlet_Validate_EmailAvailable extends Zend_Validate_Abstract {
    const NOT_AVAILABLE = 'notAvailable';

    protected $_messageTemplates = array(
        self::NOT_AVAILABLE => "Email address '%value%' is already in use"
    );

    private $repo;

    public function __construct(EntityRepository $repo) {
        $this->repo = $repo;
    }

    /**
     * Returns true if and only if $value meets the validation requirements
     *
     * If $value fails validation, then this method returns false, and
     * getMessages() will return an array of messages that explain why the
     * validation failed.
     *
     * @param  mixed $value
     * @return boolean
     * @throws Zend_Validate_Exception If validation of $value is impossible
     */
    public function isValid($value) {
        $this->_setValue($value);

        if($this->repo->findOneByEmail($value)) {
            $this->_error(self::NOT_AVAILABLE, $value);
            return false;
        }

        return true;
    }
}