FastAPI-SQLAlchemy
FastAPI-SQLAlchemy provides a simple integration between FastAPI and SQLAlchemy in your application. It gives access to useful helpers to facilitate the completion of common tasks.
Installing
Install and update using pip:
$ pip install fastapi-sqlalchemy
Examples
Usage inside of a route
from fastapi import FastAPI
from fastapi_sqlalchemy import DBSessionMiddleware # middleware helper
from fastapi_sqlalchemy import db # an object to provide global access to a database session
from app.models import User
app = FastAPI()
app.add_middleware(DBSessionMiddleware, db_url="sqlite://")
# once the middleware is applied, any route can then access the database session
# from the global ``db``
@app.get("/users")
def get_users():
users = db.session.query(User).all()
return users
Note that the session object provided by db.session is based on the Python3.7+ ContextVar. This means that each session is linked to the individual request context in which it was created.
Usage outside of a route
Sometimes it is useful to be able to access the database outside the context of a request, such as in scheduled tasks which run in the background:
import pytz
from apscheduler.schedulers.asyncio import AsyncIOScheduler # other schedulers are available
from fastapi import FastAPI
from fastapi_sqlalchemy import db
from app.models import User, UserCount
app = FastAPI()
app.add_middleware(DBSessionMiddleware, db_url="sqlite://")
@app.on_event('startup')
async def startup_event():
scheduler = AsyncIOScheduler(timezone=pytz.utc)
scheduler.start()
scheduler.add_job(count_users_task, "cron", hour=0) # runs every night at midnight
def count_users_task():
"""Count the number of users in the database and save it into the user_counts table."""
# we are outside of a request context, therefore we cannot rely on ``DBSessionMiddleware``
# to create a database session for us. Instead, we can use the same ``db`` object and
# use it as a context manager, like so:
with db():
user_count = db.session.query(User).count()
db.session.add(UserCount(user_count))
db.session.commit()
# no longer able to access a database session once the db() context manager has ended
return users
![[Question] startup and shutdown: AttributeError: type object 'DBSession' has no attribute 'connected'](https://avatars.githubusercontent.com/u/1273014?v=4)
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