From ce8ecb5f5bdbcc7144efa3ba217f6de58680d16d Mon Sep 17 00:00:00 2001
From: Tanbir Hossain Ramim <96797470+TanbirRamim@users.noreply.github.com>
Date: Sun, 13 Sep 2026 02:09:51 +0200
Subject: [PATCH] fix(event_handler): match generic alias response models in
 OpenAPI schema

Custom responses are deep-copied before resolving their model, and
deepcopy returns a new object for generic aliases such as list[Model].
The identity check against response_extra_models never matched, so
schema generation raised StopIteration. Compare by equality instead.

Fixes #8450
---
 .../event_handler/openapi/schema_generator.py |  2 +-
 .../_pydantic/test_openapi_responses.py       | 37 +++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/aws_lambda_powertools/event_handler/openapi/schema_generator.py b/aws_lambda_powertools/event_handler/openapi/schema_generator.py
index 096780996f9..0d3de7e1f8c 100644
--- a/aws_lambda_powertools/event_handler/openapi/schema_generator.py
+++ b/aws_lambda_powertools/event_handler/openapi/schema_generator.py
@@ -538,7 +538,7 @@ def _resolve_response_payload(
     model_payload_typed = cast(OpenAPIResponseContentModel, payload)
     return_field = next(
         filter(
-            lambda model: model.type_ is model_payload_typed["model"],
+            lambda model: model.type_ == model_payload_typed["model"],
             dependant.response_extra_models,
         ),
     )
diff --git a/tests/functional/event_handler/_pydantic/test_openapi_responses.py b/tests/functional/event_handler/_pydantic/test_openapi_responses.py
index c00b4e00462..3ccb4a73c94 100644
--- a/tests/functional/event_handler/_pydantic/test_openapi_responses.py
+++ b/tests/functional/event_handler/_pydantic/test_openapi_responses.py
@@ -456,3 +456,40 @@ def patch():
     assert 204 in schema.paths["/items"].put.responses
     assert 204 in schema.paths["/items"].delete.responses
     assert 202 in schema.paths["/items"].patch.responses
+
+
+def test_openapi_custom_response_with_generic_alias_models():
+    # GIVEN routes whose custom response models are generic aliases
+    app = APIGatewayRestResolver(enable_validation=True)
+
+    class Item(BaseModel):
+        id: int
+
+    @app.get(
+        "/items",
+        responses={200: {"description": "List of items", "content": {"application/json": {"model": list[Item]}}}},
+    )
+    def list_items() -> list[Item]:
+        return []
+
+    @app.get(
+        "/items/by-name",
+        responses={200: {"description": "Items by name", "content": {"application/json": {"model": dict[str, Item]}}}},
+    )
+    def items_by_name() -> dict[str, Item]:
+        return {}
+
+    # WHEN we retrieve the OpenAPI schema
+    schema = app.get_openapi_schema()
+
+    # THEN the list model should produce an array schema
+    list_response = schema.paths["/items"].get.responses[200]
+    assert list_response.description == "List of items"
+    list_schema = list_response.content["application/json"].schema_
+    assert list_schema.type == "array"
+    assert list_schema.items.ref == "#/components/schemas/Item"
+
+    # AND the dict model should produce an object schema
+    dict_schema = schema.paths["/items/by-name"].get.responses[200].content["application/json"].schema_
+    assert dict_schema.type == "object"
+    assert dict_schema.additionalProperties.ref == "#/components/schemas/Item"