Flask teardown request equivalent in Fastapi

[maxwelldorliea]

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Example Code

# Flask Implementation

from models import storage
.....
.....

@app.teardown_request
def close_session(exception=None):
    storage.close_session()

Description

I am building a rest api with fastapi. I implemented the data layer separately from the fastapi application meaning I do not have direct access to the database session in my fastapi application.

I have access to the storage object which have method like close_session which allow me to close the current session.

Is there a equivalent of flask teardown_request in fastapi?

I have looked at fastapi on_event('shutdown') and on_event('startup'). These two only runs when the application is shutting down or starting up.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.92.0

Python Version

3.8.10

Additional Context

No response

[williamjamir]

It is possible to have a teardown request in FastAPI by using a Dependency. Here is an example:

from fastapi import FastAPI, Depends

app = FastAPI()

async def some_func():
    print('Up')
    try:
        yield
    finally:
        print('Teardown')

@app.get('/')
async def some_router_func(foo=Depends(some_func)):
    print('Some code')

if __name__ == '__main__':
    import uvicorn
    uvicorn.run('x:app')

When you run this code and make a GET request to '/', you will see the following output in your console:

INFO:     Started server process [14025]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Up
Some code
INFO:     127.0.0.1:49389 - "GET / HTTP/1.1" 200 OK
Teardown


Up
Some code
INFO:     127.0.0.1:49393 - "GET / HTTP/1.1" 200 OK
Teardown

As you can see, the some_func function is executed, and everything before the yield is called at the begging of the request.

After the request has been finished (everything from the function was executed), the code after the yield is executed (acting exactly as a teardown).

I hope this helps!

[maxwelldorliea]

How can I do this for all request without manually doing it for each route?

[williamjamir]

You can easily apply a dependency for the whole project using the FastAPI constructor.

app = FastAPI(dependencies=[Depends(some_func)])

Or segment by router ;)

router = APIRouter(
    dependencies=[Depends(some_func)],
)

@router.get
...

Let me know if this answers your question :)

[maxwelldorliea]

Thanks

[crazydevlegend]

how can i use that dependency in a method?

[ondiekisteven]

I think middlewares run after this code. it's not the last code to be run