- Added partial support for Index as primary keys

src/Common/EntityResolver.php

@@ -5,6 +5,7 @@ namespace Ulmus\Common;
 use Notes\Common\ReflectedClass;
 use Notes\Common\ReflectedProperty;
 use Psr\SimpleCache\CacheInterface;
+use Ulmus\Attribute\Obj\Index;
 use Ulmus\Ulmus,
     Ulmus\Attribute\Obj\Table,
     Ulmus\Attribute\Obj\AdapterAttributeInterface,
@@ -214,9 +215,9 @@ class EntityResolver {
         return null;
     }
     
-    public function getCompoundKeyFields() : ? array
+    public function getCompoundKeyFields() : ? Index
     {
-        return null;
+        return $this->getAttributeImplementing(Index::class);
     }
     
     public function getUniqueFields() : ? array