fastapi-routechain

Combine multiple APIRoute subclasses for FastAPI — with automatic conflict detection.

Installation

pip install fastapi-routechain

The problem

FastAPI's APIRouter accepts only a single route_class. If you want to use multiple third-party route classes together (e.g. DishkaRoute for DI and XmlRoute for XML support), you'd have to manually create a combined class.

Usage

ChainedAPIRouter — drop-in replacement for APIRouter

from fastapi_routechain import ChainedAPIRouter
from dishka.integrations.fastapi import DishkaRoute
from fastapi_xml import XmlRoute

router = ChainedAPIRouter(
    route_classes=[DishkaRoute, XmlRoute],  # priority = list order (MRO)
)

@router.get("/hello")
def hello():
    return {"hello": "world"}

combine_routes — just the factory

from fastapi import APIRouter
from fastapi_routechain import combine_routes

MyRoute = combine_routes(DishkaRoute, XmlRoute)

router = APIRouter(route_class=MyRoute)

Priority and MRO

The order of classes in route_classes is the priority order — it directly maps to Python's MRO (Method Resolution Order). The first class wins on conflicts.

# DishkaRoute.__init__ takes priority over XmlRoute.__init__
combine_routes(DishkaRoute, XmlRoute)

Conflict detection

fastapi-routechain warns you when combining classes that will silently lose functionality — e.g. two classes that both override get_route_handler without calling super().

# emits RouteConflictWarning
combine_routes(XmlRoute, SomeOtherHandlerRoute)

# raises RouteConflictError instead
combine_routes(XmlRoute, SomeOtherHandlerRoute, strict=True)

You can also check conflicts manually:

from fastapi_routechain import check_conflicts

issues = check_conflicts(RouteA, RouteB, RouteC)
for issue in issues:
    print(issue)

API