Fix unique operation IDs for multi-method routes

fastapi/openapi/utils.py

@@ -233,6 +233,13 @@ def generate_operation_summary(*, route: routing.APIRoute, method: str) -> str:
     return route.name.replace("_", " ").title()
 
 
+def get_openapi_operation_id(*, route: routing.APIRoute, method: str) -> str:
+    operation_id = route.operation_id or route.unique_id
+    if route.operation_id is None and route.methods and len(route.methods) > 1:
+        operation_id = f"{operation_id}_{method.lower()}"
+    return operation_id
+
+
 def get_openapi_operation_metadata(
     *, route: routing.APIRoute, method: str, operation_ids: set[str]
 ) -> dict[str, Any]:
@@ -242,7 +249,7 @@ def get_openapi_operation_metadata(
     operation["summary"] = generate_operation_summary(route=route, method=method)
     if route.description:
         operation["description"] = route.description
-    operation_id = route.operation_id or route.unique_id
+    operation_id = get_openapi_operation_id(route=route, method=method)
     if operation_id in operation_ids:
         endpoint_name = getattr(route.endpoint, "__name__", "<unnamed_endpoint>")
         message = f"Duplicate Operation ID {operation_id} for function {endpoint_name}"

fastapi/utils.py

@@ -96,7 +96,8 @@ def generate_unique_id(route: "APIRoute") -> str:
     operation_id = f"{route.name}{route.path_format}"
     operation_id = re.sub(r"\W", "_", operation_id)
     assert route.methods
-    operation_id = f"{operation_id}_{list(route.methods)[0].lower()}"
+    if len(route.methods) == 1:
+        operation_id = f"{operation_id}_{sorted(route.methods)[0].lower()}"
     return operation_id
 
 

tests/test_generate_unique_id_function.py

@@ -1697,3 +1697,44 @@ def test_warn_duplicate_operation_id():
         ]
         assert len(duplicate_warnings) > 0
         assert "Duplicate Operation ID" in str(duplicate_warnings[0].message)
+
+
+def test_multi_method_route_unique_operation_ids():
+    app = FastAPI()
+
+    @app.api_route("/clear", methods=["POST", "DELETE"])
+    def clear():
+        return None  # pragma: nocover
+
+    client = TestClient(app)
+    with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("always")
+        response = client.get("/openapi.json")
+        assert response.status_code == 200, response.text
+
+    duplicate_warnings = [
+        warning
+        for warning in w
+        if issubclass(warning.category, UserWarning)
+        and "Duplicate Operation ID" in str(warning.message)
+    ]
+    assert duplicate_warnings == []
+    path = response.json()["paths"]["/clear"]
+    assert path["post"]["operationId"] == "clear_clear_post"
+    assert path["delete"]["operationId"] == "clear_clear_delete"
+
+
+def test_multi_method_route_unique_operation_ids_with_custom_generate_unique_id():
+    app = FastAPI(generate_unique_id_function=custom_generate_unique_id)
+
+    @app.api_route("/clear", methods=["POST", "DELETE"])
+    def clear():
+        return None  # pragma: nocover
+
+    client = TestClient(app)
+    response = client.get("/openapi.json")
+
+    assert response.status_code == 200, response.text
+    path = response.json()["paths"]["/clear"]
+    assert path["post"]["operationId"] == "foo_clear_post"
+    assert path["delete"]["operationId"] == "foo_clear_delete"