From 1b535d1076fe99ba7d2e334a179e13efa481d080 Mon Sep 17 00:00:00 2001
From: Rob Percival <rob.percival@octoenergy.com>
Date: Fri, 6 May 2022 17:06:34 +0100
Subject: [PATCH] Add GenericModel to types

Provides a workaround for a bug in Django that prevents models from
inheriting from Generic.
---
 xocto/types.py | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/xocto/types.py b/xocto/types.py
index 027b5e2..63b98e8 100644
--- a/xocto/types.py
+++ b/xocto/types.py
@@ -2,7 +2,7 @@
 Utility types to save having to redefine the same things over and over.
 """
 
-from typing import Generic, NoReturn, Tuple, TypeVar, Union
+from typing import TYPE_CHECKING, Generic, NoReturn, Tuple, TypeVar, Union
 
 from django.contrib.auth import models as auth_models
 from django.db import models
@@ -63,6 +63,22 @@ class AuthenticatedRequest(HttpRequest, Generic[User]):
     user: User
 
 
+# Django does not like models which inherit from Generic.
+# This is the recommended workaround (https://code.djangoproject.com/ticket/33174).
+if TYPE_CHECKING:
+
+    U = TypeVar("U")
+
+    class GenericModel(models.Model, Generic[U]):
+        pass
+
+else:
+
+    class GenericModel(models.Model):
+        def __class_getitem__(cls, _):  # noqa: K106
+            return cls
+
+
 def assert_never(value: NoReturn) -> NoReturn:
     """
     Helper to ensure checks are exhaustive.