at the end of the day, it was inevitable

src/ApiBundle/Entity/NormalizableEntityInterface.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace ApiBundle\Entity;
+
+/**
+ * Interface NormalizableEntityInterface
+ * @package ApiBundle\Entity
+ */
+interface NormalizableEntityInterface
+{
+
+    /**
+     * Return metadata for current entity.
+     *
+     * @return \ApiBundle\Serializer\Metadata\Metadata
+     */
+    public function getMetadata();
+
+    /**
+     * Return default normalization groups.
+     *
+     * @return array
+     */
+    public function defaultGroups();
+}