From 14d13b3036f958fdfb86c95bf2e99bdf189a4983 Mon Sep 17 00:00:00 2001
From: Sam Partington <sam@whiteoctober.co.uk>
Date: Wed, 30 Jan 2013 11:20:36 +0000
Subject: [PATCH] Now correctly handles UniqueDocument criteria which are
 references to other Documents.

Without this, you'll see the Mongo error 'zero-length keys are not allowed, did you use $ with double quotes?' as it doesn't know how to handle the document.
---
 Validator/Constraint/UniqueDocumentValidator.php | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Validator/Constraint/UniqueDocumentValidator.php b/Validator/Constraint/UniqueDocumentValidator.php
index 9b77a3e..4aca6c0 100644
--- a/Validator/Constraint/UniqueDocumentValidator.php
+++ b/Validator/Constraint/UniqueDocumentValidator.php
@@ -116,6 +116,9 @@ private function createCriteria(Document $document, array $fields, array $caseIn
         $criteria = array();
         foreach ($fields as $field) {
             $value = $document->get($field);
+            if ($value instanceof Document) {
+                $value = $value->getId();
+            }
             if (in_array($field, $caseInsensitive)) {
                 $value = new \MongoRegex(sprintf('/^%s$/i', $value));
             }