From 3c100f28661f3440769175a17c2763ed25f4b83a Mon Sep 17 00:00:00 2001
From: Ethan Langevin <ethan.langevin@anthropic.com>
Date: Wed, 6 Mar 2024 20:18:30 -0500
Subject: [PATCH] Fixes: #11112 - Make instrumented attribute covariant as well

---
 lib/sqlalchemy/orm/attributes.py              |  2 +-
 .../plain_files/orm/mapped_covariant.py       | 25 ++++++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index d9b2d8213d..d3d773055b 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -503,7 +503,7 @@ def _queryable_attribute_unreduce(
         return getattr(entity, key)
 
 
-class InstrumentedAttribute(QueryableAttribute[_T]):
+class InstrumentedAttribute(QueryableAttribute[_T_co]):
     """Class bound instrumented attribute which adds basic
     :term:`descriptor` methods.
 
diff --git a/test/typing/plain_files/orm/mapped_covariant.py b/test/typing/plain_files/orm/mapped_covariant.py
index 9f964021b3..398db309fb 100644
--- a/test/typing/plain_files/orm/mapped_covariant.py
+++ b/test/typing/plain_files/orm/mapped_covariant.py
@@ -2,12 +2,15 @@
 
 from datetime import datetime
 from typing import Protocol
+from typing import Sequence
+from typing import TypeVar
 from typing import Union
 
 from sqlalchemy import ForeignKey
 from sqlalchemy import func
 from sqlalchemy import Nullable
 from sqlalchemy.orm import DeclarativeBase
+from sqlalchemy.orm import InstrumentedAttribute
 from sqlalchemy.orm import Mapped
 from sqlalchemy.orm import mapped_column
 from sqlalchemy.orm import relationship
@@ -24,7 +27,8 @@ class ChildProtocol(Protocol):
     # Read-only for simplicity, mutable protocol members are complicated,
     # see https://mypy.readthedocs.io/en/latest/common_issues.html#covariant-subtyping-of-mutable-protocol-members-is-rejected
     @property
-    def parent(self) -> Mapped[ParentProtocol]: ...
+    def parent(self) -> Mapped[ParentProtocol]:
+        ...
 
 
 def get_parent_name(child: ChildProtocol) -> str:
@@ -43,6 +47,8 @@ class Parent(Base):
 
     name: Mapped[str] = mapped_column(primary_key=True)
 
+    children: Mapped[Sequence["Child"]] = relationship("Child")
+
 
 class Child(Base):
     __tablename__ = "child"
@@ -55,6 +61,23 @@ class Child(Base):
 
 assert get_parent_name(Child(parent=Parent(name="foo"))) == "foo"
 
+# Make sure that relationships are covariant as well
+_BaseT = TypeVar("_BaseT", bound=Base, covariant=True)
+RelationshipType = (
+    InstrumentedAttribute[_BaseT]
+    | InstrumentedAttribute[Sequence[_BaseT]]
+    | InstrumentedAttribute[_BaseT | None]
+)
+
+
+def operate_on_relationships(
+    relationships: list[RelationshipType[_BaseT]],
+) -> int:
+    return len(relationships)
+
+
+assert operate_on_relationships([Parent.children, Child.parent]) == 2
+
 # other test
 
 
-- 
2.47.2