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@tafaust
Created April 21, 2022 19:41
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FastAPI singleton service dependency injection across multiple requests
import random
import click
import uvicorn
from fastapi import FastAPI, APIRouter, Depends, Request
# Service
class MySingletonService:
def __init__(self):
self.random_number = random.randint(1, 100)
def __str__(self):
return 'my_singleton_service'
def say_hello(self) -> str:
return f'Hello Python Community! You will see "{self.random_number}" for every request.'
# Helper to grab dependencies that live in the app.state
def get_my_singleton_service(request: Request) -> MySingletonService:
# See application for the key name in `app`.
return request.app.state.my_singleton_service
# Router
router = APIRouter(prefix='/linkedin', tags=['LinkedIn'])
@router.get('/hello_python', response_model=str)
async def edge_detection(my_singleton_service: MySingletonService = Depends(get_my_singleton_service)) -> str:
return my_singleton_service.say_hello()
# FastAPI Application Factory
def create_app() -> FastAPI:
"""Creates the FastAPI application.
"""
application = FastAPI(title='This is single-instance DI across requests!')
application.include_router(router=router)
# Register our singleton service for DI once when the app has finished startup
@application.on_event('startup')
def load_single_instance_service():
application.state.my_singleton_service = MySingletonService()
return application
@click.command()
@click.option('--host', default='127.0.0.1', help='host')
@click.option('--port', default='31313', help='port')
@click.option('--hot-reload', is_flag=True, default=False, help='Hot reload')
@click.option('--log-level', default='info', help='Set the log level. Default: "info".')
def main(host, port, hot_reload, log_level):
uvicorn.run('application:create_app', host=host, port=int(port), reload=hot_reload, log_level=log_level, factory=True)
if __name__ == '__main__':
main()
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