Doctrine2 Zend_Validate_DbRecord_NotExists (Gamempire\Validate\Entity\Field\Unique) implementation

Unique.php

<?php
namespace Gamempire\Validate\Entity\Field;

/**
 * Validates input entity field to check if it is unique
 *
 * @author Ocramius
 */
class Unique extends \Zend_Validate_Abstract {

    /**
     * Error constants
     */
    const ERROR_RECORD_FOUND    = 'recordFound';

    /**
     * @var array Message templates
     */
    protected $_messageTemplates = array(
        self::ERROR_RECORD_FOUND    => 'Duplicate \'%value%\'',
    );

    /**
     *
     * @var \Doctrine\ORM\EntityManager
     */
    protected $_em;

    /**
     *
     * @var \Gamempire\Entity
     */
    protected $_matchedEntity;

    /**
     *
     * @var string
     */
    protected $_matchedEntityClass;

    /**
     *
     * @var string
     */
    protected $_field;

    public function __construct(\Doctrine\ORM\EntityManager $em, \Gamempire\Entity $matchedEntity, $field) {
        $this->_em = $em;
        $this->_field = $field;
        $this->_matchedEntity = $matchedEntity;
        $metadata = $this
            ->_em
            ->getMetadataFactory()
            ->getMetadataFor(\get_class($this->_matchedEntity));
        $this->_matchedEntityClass = $metadata->reflClass->getName();
        if(!\is_string($field)) {
            throw new \Zend_Validate_Exception('Provided parameter $field must be a string!');
        }
        try {
            if(!$metadata->getFieldMapping($field)) {
                throw new \Zend_Validate_Exception('Matched entity does not contain field \'' . $field . '\'!');
            }
        }catch(\Exception $e) {
            throw new \Zend_Validate_Exception('Matched entity does not contain field \'' . $field . '\'!', 0, $e);
        }
    }

    public function isValid($value) {
        if(
            \is_object($value)
            && $value instanceof \Gamempire\Entity
        ) {
            if(!($value instanceof $this->_matchedEntityClass)) {
                throw new \Zend_Validate_Exception('Value to be validated must be an instance of \'' . $this->_matchedEntityClass . '\'!');
            }
            $value = $value[$this->_field];
        }
        $this->_setValue($value);
        if(
            $match = $this
                ->_em
                ->getRepository($this->_matchedEntityClass)
                ->findOneBy(array($this->_field => $value))
        ) {
            if($match->id !== $this->_matchedEntity->id) {
                $this->_error(self::ERROR_RECORD_FOUND);
                return false;
            }
        }
        return true;
    }

}