FOS\UserBundle\Document\UserManager::validateUnique PHP Method

    public function validateUnique($value, Constraint $constraint)
    {
        $classMetadata = $this->dm->getClassMetadata($this->class);
        // TODO: ODM seems to be missing handling for multiple properties
        // $fields = array_map('trim', explode(',', $constraint->property));
        $query = $this->getQueryArray($classMetadata, $value, $constraint->property);
        $document = $this->findUserBy($query);
        if (null === $document) {
            return true;
        }
        // check if document in mongodb is the same document as the checked one
        if ($document->isUser($value)) {
            return true;
        }
        // check if returned document is proxy and initialize the minimum identifier if needed
        if ($document instanceof Proxy) {
            $classMetadata->setIdentifierValue($document, $document->__identifier);
        }
        // check if document has the same identifier as the current one
        if ($classMetadata->getIdentifierValue($document) === $classMetadata->getIdentifierValue($value)) {
            return true;
        }
        return false;
    }