fix(event_handler): add middleware validation per route

aws_lambda_powertools/event_handler/api_gateway.py

@@ -546,6 +546,19 @@ def _build_middleware_stack(self, router_middlewares: list[Callable[..., Any]],
             self.enable_validation if self.enable_validation is not None else app._enable_validation
         )
 
+        # If route needs validation but resolver didn't create the middlewares, create them now
+        if route_validation_enabled and not hasattr(app, "_request_validation_middleware"):
+            from aws_lambda_powertools.event_handler.middlewares.openapi_validation import (
+                OpenAPIRequestValidationMiddleware,
+                OpenAPIResponseValidationMiddleware,
+            )
+
+            app._request_validation_middleware = OpenAPIRequestValidationMiddleware()
+            app._response_validation_middleware = OpenAPIResponseValidationMiddleware(
+                validation_serializer=app._serializer,
+                has_response_validation_error=app._has_response_validation_error,
+            )
+
         # Add request validation middleware first if validation is enabled
         if route_validation_enabled and hasattr(app, "_request_validation_middleware"):
             all_middlewares.append(app._request_validation_middleware)

tests/functional/event_handler/_pydantic/test_per_route_validation.py

@@ -240,8 +240,8 @@ def invalid_response() -> TodoItem:
 
 
 def test_per_route_validation_with_pydantic_v2():
-    """Test that per-route validation works correctly with Pydantic v2 models"""
-    # GIVEN APIGatewayRestResolver with mixed validation
+    """Test that per-route validation actually validates when resolver has validation disabled"""
+    # GIVEN APIGatewayRestResolver WITHOUT global validation
     app = APIGatewayRestResolver()
 
     class Task(BaseModel):
@@ -250,7 +250,8 @@ class Task(BaseModel):
 
     @app.get("/task", enable_validation=True)
     def get_task() -> Task:
-        return Task(title="Important", priority=1)
+        # Return invalid data — missing 'title' and 'priority'
+        return cast(Task, {"wrong": "data"})
 
     @app.get("/unvalidated-task")
     def get_unvalidated_task():
@@ -259,13 +260,12 @@ def get_unvalidated_task():
     event = load_event("apiGatewayProxyEvent.json")
     event["httpMethod"] = "GET"
 
-    # WHEN calling validated route
+    # WHEN calling validated route with invalid data
     event["path"] = "/task"
     result = app(event, {})
 
-    # THEN should validate and serialize correctly
-    assert result["statusCode"] == 200
-    assert "Important" in result["body"]
+    # THEN validation must reject it with 422
+    assert result["statusCode"] == 422
 
     # WHEN calling unvalidated route
     event["path"] = "/unvalidated-task"
@@ -274,3 +274,28 @@ def get_unvalidated_task():
     # THEN should return as-is without validation
     assert result["statusCode"] == 200
     assert "extra" in result["body"]
+
+
+def test_per_route_opt_in_validation_with_valid_data():
+    """Test that per-route opt-in validation passes valid data and serializes correctly"""
+    # GIVEN APIGatewayRestResolver WITHOUT global validation
+    app = APIGatewayRestResolver()
+
+    class Task(BaseModel):
+        title: str
+        priority: int
+
+    @app.get("/task", enable_validation=True)
+    def get_task() -> Task:
+        return Task(title="Important", priority=1)
+
+    event = load_event("apiGatewayProxyEvent.json")
+    event["httpMethod"] = "GET"
+    event["path"] = "/task"
+
+    # WHEN calling validated route with valid data
+    result = app(event, {})
+
+    # THEN validation passes and response is serialized
+    assert result["statusCode"] == 200
+    assert "Important" in result["body"]