Application Lifecycle

Nexios Application Lifecycle

Introduction

Nexios provides multiple ways to manage application initialization and cleanup:

1. Decorators:

   • on_startup: Functions to run at application startup.

   • on_shutdown: Functions to run at application shutdown.

2. Lifespan Async Context Manager: A single async context manager to handle both startup and shutdown logic.

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Application Startup

The @app.on_startup() decorator registers functions that should execute when the Nexios application starts. This is useful for initializing databases, setting up cache systems, or loading configuration settings.

Example: Initialize Database on Startup

from nexios import get_application
from tortoise import Tortoise
from config import DATABASE_CONFIG

app = get_application()

async def init_db():
    await Tortoise.init(config=DATABASE_CONFIG)
    await Tortoise.generate_schemas()

@app.on_startup()
async def startup():
    await init_db()
    print("Application started successfully!")

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Application Shutdown

The @app.on_shutdown() decorator registers functions to execute when the application shuts down. This is useful for closing database connections, clearing cache, or performing cleanup tasks.

Example: Closing Database Connections on Shutdown

@app.on_shutdown()
async def shutdown():
    await Tortoise.close_connections()
    print("Application shutting down...")

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Lifespan Async Context Manager

Nexios also supports using an asynchronous context manager to handle both startup and shutdown events in a single construct. This is achieved by defining a lifespan function and passing it to the application via the lifespan argument. This approach encapsulates initialization and cleanup logic in one place.

Example: Using Lifespan for Database Initialization and Cleanup

from nexios import get_application
from contextlib import asynccontextmanager
from tortoise import Tortoise
from config import DATABASE_CONFIG

@asynccontextmanager
async def app_lifespan(app):
    # Application startup logic
    await Tortoise.init(config=DATABASE_CONFIG)
    await Tortoise.generate_schemas()
    print("Application started successfully!")
    yield
    # Application shutdown logic
    await Tortoise.close_connections()
    print("Application shutting down...")

app = get_application(lifespan=app_lifespan)

Key Notes:

• The lifespan parameter accepts an async context manager that handles both startup (before yield) and shutdown (after yield).

• Avoid combining this method with @app.on_startup()/@app.on_shutdown() decorators for the same tasks to prevent redundant execution.

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By leveraging on_startup, on_shutdown, or the lifespan async context manager, developers can ensure resources are properly initialized and cleaned up, leading to stable and maintainable Nexios applications.