# UNDF: UNDF-2026-000000052
Fixes doctrine-0003: SqlWalker::walkObjectExpression in_array per field.

--- a/src/Doctrine/ORM/Query/SqlWalker.php
+++ b/src/Doctrine/ORM/Query/SqlWalker.php

@@ DEFECT doctrine-0003: SqlWalker.php:1405,1445 walkObjectExpression()

     private function walkObjectExpression(...): string
     {
+        // FIX doctrine-0003: convert partialFieldSet from array to set for O(1) lookup.
+        // Previously: in_array($fieldName, $partialFieldSet) is O(|partialFieldSet|) per field.
+        // Called for every fieldMapping in every class/subclass in the DQL result.
+        $partialFieldSetFlip = $partialFieldSet !== null ? array_flip($partialFieldSet) : null;

         foreach ($class->fieldMappings as $fieldName => $mapping) {
-            if ($partialFieldSet && ! in_array($fieldName, $partialFieldSet, true)) {
+            if ($partialFieldSetFlip !== null && ! isset($partialFieldSetFlip[$fieldName])) {
                 continue;
             }
             // ... build SQL
         }

         foreach ($subClass->fieldMappings as $fieldName => $mapping) {
-            if (isset($mapping->inherited) || ($partialFieldSet && ! in_array($fieldName, $partialFieldSet, true))) {
+            if (isset($mapping->inherited) || ($partialFieldSetFlip !== null && ! isset($partialFieldSetFlip[$fieldName]))) {
                 continue;
             }
         }
     }

# BEFORE: in_array($field, $partialFieldSet) — O(P) per field across all mappings.
#         Total: O(F × P) for F field mappings, P partial field set size.
# AFTER:  isset($partialFieldSetFlip[$field]) — O(1).
# Triggered by: any DQL query using SELECT PARTIAL entity.{field1,field2,...}.