# UNDF: UNDF-2026-000000051
Fixes doctrine-0002: ClassMetadata::addSubClass in_array dedup.

--- a/src/Doctrine/ORM/Mapping/ClassMetadata.php
+++ b/src/Doctrine/ORM/Mapping/ClassMetadata.php

@@ DEFECT doctrine-0002: ClassMetadata.php:2313 addSubClass()

+    /** @var array<string, true>  FIX doctrine-0002: hash set for O(1) subclass dedup */
+    public array $subClassesSet = [];

     public function addSubClass(string $className): void
     {
-        if (is_subclass_of($className, $this->name) && ! in_array($className, $this->subClasses, true)) {
-            $this->subClasses[] = $className;
+        // FIX doctrine-0002: replace O(S) in_array scan with O(1) hash check.
+        if (is_subclass_of($className, $this->name) && ! isset($this->subClassesSet[$className])) {
+            $this->subClasses[] = $className;
+            $this->subClassesSet[$className] = true;
         }
     }

# BEFORE: in_array($className, $this->subClasses) — O(S) per addSubClass call.
#         ClassMetadataFactory calls addSubClass in loops over parent hierarchies.
#         Total: O(H × S) where H = hierarchy depth, S = subclass count.
# AFTER:  isset($this->subClassesSet[$className]) — O(1).
# Triggered by: application startup / metadata cache warming.