diff --git a/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php b/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
index 0bd9505a6..eaa7b6c72 100644
--- a/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
+++ b/src/Bundle/ChillMainBundle/Doctrine/ORM/Hydration/FlatHierarchyEntityHydrator.php
@@ -16,33 +16,33 @@ final class FlatHierarchyEntityHydrator extends ObjectHydrator
         return array_values(iterator_to_array($this->flatListGenerator($this->buildChildrenHashmap(parent::hydrateAllData()))));
     }
 
-    private function flatListGenerator(array $hashMap, $parent = null): Generator
+    private function flatListGenerator(array $hashMap, ?int $parent = null): Generator
     {
-        $parent = null === $parent ?
-            null :
-            spl_object_hash($parent);
+        $parent ??= spl_object_id($parent);
 
         $hashMap += [$parent => []];
 
         foreach ($hashMap[$parent] as $node) {
-            yield $node->getId() => $node;
+            yield spl_object_id($node) => $node;
             yield from $this->flatListGenerator($hashMap, $node);
         }
     }
 
     private function buildChildrenHashmap(array $nodes): array
     {
-        $r = [];
+        return array_reduce(
+            $nodes,
+            static function (array $collect, $node) {
+                $parentId = (null === $parent = $node->getParent()) ?
+                    null :
+                    spl_object_id($parent);
 
-        foreach ($nodes as $node) {
-            $parentId = (null !== $parent = $node->getParent())
-                ? spl_object_hash($parent)
-                : null;
+                $collect[$parentId][] = $node;
 
-            $r[$parentId][] = $node;
-        }
-
-        return $r;
+                return $collect;
+            },
+            []
+        );
     }
 
 }