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Routers and Sub-Applications ​

Nexios provides a powerful routing system that allows you to create modular and nested routing structures. Here's an example of how you can use routers and sub-applications in your application

Creating a Router and Mounting it to the Main Application ​

python
from nexios import NexiosApp
from nexios.routing import Router

app = NexiosApp()

v1_router = Router(prefix="/v1")

@v1_router.get("/users")
async def list_users(req, res):
    return res.json({"message": "List of users"})

@v1_router.get("/users/{user_id}")
async def get_user(req, res, user_id):
    return res.json({"user_id": user_id})

app.mount_router(v1_router)

Overriding Prefix at Mount Time You can override the default router prefix when mounting it to the app. This is helpful when reusing a router module in multiple places.

py
app.mount_router(v1_router, prefix="/api/v1")

Tip 💡

he prefix in mount_router always takes precedence over the one set in the Router instance.

This example creates a router with two routes, one for listing users and another for getting a specific user. The router is then mounted to the main application using the mount_router method.

This matches /v1/users and /v1/users/{user_id}

⚠️ Bug Alert

Ensure to use mount_router after all routes have been defined.

What is Router? ​

A Router is a container for routes and sub-applications. It allows you to create a modular and nested routing structure in your application.

⚠️ Bug Alert

Ensure all mounted sub application or sub-routers have unique prefixes

Routers can contain other routers. This is useful when you want even finer modularization, e.g., versioned APIs with internal domains.

python

app = NexiosApp()

v1_router = Router(prefix="/v1")
user_router = Router(prefix="/users")

@user_router.get("/")
async def index(req, res):
    return res.text("User root")

@user_router.get("/{id}")
async def detail(req, res, id):
    return res.json({"user": id})

# Mount user_router inside v1_router
v1_router.mount_router(user_router)

# Mount v1_router into the app
app.mount_router(v1_router)

Now, the final paths are:

  • /v1/users/

  • /v1/users/{id}

You can nest as deeply as you want. Internally, Nexios flattens the route tree during app startup for performance.

The Router class also have similar routing methods as NexiosApp class

Sub-Applications = Routers ​

NexiosApp is a subclass of Router. This means you can treat entire apps as routers and mount them.

py
main_app = NexiosApp()
admin_app = NexiosApp()

@admin_app.get("/dashboard")
async def dashboard(req, res):
    return res.text("Welcome to the admin panel")

main_app.mount_router(admin_app, prefix="/admin")

Now you can access /admin/dashboard.

This makes it trivial to build modular applications where teams can work on separate parts (e.g., auth, billing, analytics) in isolation and plug them into a larger system