From 856e1ca4c1a462c399533f4f7148e7b8dfb52f14 Mon Sep 17 00:00:00 2001
From: Andrey Smakotin <slamfromm@gmail.com>
Date: Sat, 22 Nov 2025 23:33:52 +0300
Subject: [PATCH] Fix select_for_update with nullable FK outer join error
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Remove select_related('locked_by_user') from select_for_update query
to avoid PostgreSQL error "FOR UPDATE cannot be applied to the
nullable side of an outer join". Username is now fetched via lazy load.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 myproject/pos/views.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/myproject/pos/views.py b/myproject/pos/views.py
index fd8b278..774dae4 100644
--- a/myproject/pos/views.py
+++ b/myproject/pos/views.py
@@ -486,6 +486,7 @@ def add_showcase_kit_to_cart(request, kit_id):
         # Атомарная проверка и создание блокировки (предотвращает race condition)
         with transaction.atomic():
             # Блокируем строки резервов для этого комплекта на уровне БД
+            # Примечание: нельзя использовать select_related с nullable FK при select_for_update
             reservations = Reservation.objects.select_for_update().filter(
                 product_kit=kit,
                 status='reserved'
@@ -496,13 +497,15 @@ def add_showcase_kit_to_cart(request, kit_id):
                 cart_lock_expires_at__gt=timezone.now()
             ).exclude(
                 locked_by_user=request.user
-            ).select_related('locked_by_user').first()
+            ).first()
 
             if existing_lock:
+                # Получаем username отдельным запросом (избегаем outer join с select_for_update)
+                locked_by_username = existing_lock.locked_by_user.username if existing_lock.locked_by_user else 'другой кассир'
                 time_left = (existing_lock.cart_lock_expires_at - timezone.now()).total_seconds() / 60
                 return JsonResponse({
                     'success': False,
-                    'error': f'Этот букет уже в корзине кассира "{existing_lock.locked_by_user.username}". '
+                    'error': f'Этот букет уже в корзине кассира "{locked_by_username}". '
                              f'Блокировка истечет через {int(time_left)} мин.'
                 }, status=409)  # 409 Conflict