Add asynchronous sqlalchemy example

[ArcLightSlavik]

Recently sqlalchemy released the beta for the 1.4 release, which includes support for asynchronous calls.
This PR adds an example based on (https://fastapi.tiangolo.com/tutorial/sql-databases/) but with asynchronous calls.

[codecov]

Codecov Report

Attention: 148 lines in your changes are missing coverage. Please review.

Comparison is base (cf73051) 100.00% compared to head (982da54) 98.57%.
Report is 1078 commits behind head on master.

❗ Current head 982da54 differs from pull request most recent head 9c2a553. Consider uploading reports for the commit 9c2a553 to get more accurate results

Files	Patch %	Lines
docs_src/async_sql_databases/sql_app/main.py	0.00%	39 Missing ⚠️
docs_src/async_sql_databases/sql_app/crud.py	0.00%	35 Missing ⚠️
.../async_sql_databases/sql_app/tests/test_sql_app.py	0.00%	30 Missing ⚠️
docs_src/async_sql_databases/sql_app/schemas.py	0.00%	22 Missing ⚠️
docs_src/async_sql_databases/sql_app/models.py	0.00%	17 Missing ⚠️
docs_src/async_sql_databases/sql_app/database.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##            master    #2331      +/-   ##
===========================================
- Coverage   100.00%   98.57%   -1.43%     
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  Files          540      415     -125     
  Lines        13969    10412    -3557     
===========================================
- Hits         13969    10264    -3705     
- Misses           0      148     +148     

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[ArcLightSlavik]

Added an issue to pydantic for the response_model: pydantic/pydantic#2124

The test added here fails because of this issue.
Also includes a workaround if anyone is interested.

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[Kludex]

Can you push the failing commit so I can debug? 🥺

[Mause]

@ArcLightSlavik you need to use .scalars().all() instead of just .all() to fix your pydantic validation problem

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[yenchenLiu]

I found a problem, it comes from Sqlalchemy. And the problem will appear in PostgreSQL.
When the crud is operated for the second time, the first time object will become unavailable.
Because sqlalchemy need to query again, but it is not await at this time.

[ArcLightSlavik]

@yenchenLiu Haven't written about this issue here, but it's been known for weeks now. I am not sure which dependancy is at fault for it so I haven't made an issue. I assume it will be fixed in beta/release version of async alchemy.

[ArcLightSlavik]

SQLAlchemy released a 2nd beta and from my testing everything seems to be working.

@yenchenLiu Could you install SQLAlchemy==1.4.0b2 and check if the error happens, if yes could you link the code? Can't replicate it as of right now.

[jokull]

Did a quick test but SQLAlchemy complained that the default sqlite driver was not async. Does there even exist an async sqlite driver?

[gerazenobi]

FYI: SQLAlchemy 1.4 has just been released.

@jokull from the release docs I think not:

Complete support for Python asyncio for both Core and ORM. This new system leverages the greenlet context-switching library to adapt the entirety of SQLAlchemy to be usable behind a very thin asyncio front-end while operating directly against asyncio database drivers within the asyncio event loop, with no need for thread executors. Support for asyncpg and aiomysql is included so far with more drivers in development.

[kurtrottmann]

Hi @ArcLightSlavik,

I tried this with PostgreSQL in the past (1.4.0b1) and with SQLAlchemy 1.4.1 today, and it doesn't work properly as @yenchenLiu mentions.

A workaround I found is to use lazy='subquery' or lazy='selectin' in items relationship. Example:

items = relationship("Item", back_populates="owner", lazy='subquery')

Also is necessary to remove "check_same_thread" parameter from create_async_engine when PostgreSQL is used.

[gerazenobi]

@kurtrottmann indeed. Relationships don't work quite the same in async mode as stated in the async sqlalchemy documentation: here

[Kludex]

Maybe adding an update (put) method?

[aaronstephenson]

Thank you so much @ArcLightSlavik for writing this! It was instrumental in my attempt to get the async ORM working in my app. I hope this makes it to the official docs soon so others can benefit from it.

Also thanks to @kurtrottmann for your tips, they likely saved me a lot of time. I have several levels of nested relationships in my app, so I ended up declaring my relationships using backref and lazy=joined. Example:

items = relationship("Item", backref="owner", lazy='joined')

I did that because putting lazy in both sides of the back_populates relationship slowed the query down enormously. Maybe that's documented somewhere, but I didn't see it after doing a lot of reading, so I discovered the hard way that lazy should only be included on one side of the relationship. Declaring the relationship once with backref instead of twice with back_populates makes this more straightforward to me and my team (no need to question why the two sides of a relationship declaration have differing numbers of parameters, and a lot fewer lines of code to maintain across our many models).

[jcf-dev]

1.4.3 was released today with aiosqlite support.

[grillazz]

@ArcLightSlavik i have ready to use here solution: https://github.com/grillazz/fastapi-sqlalchemy-asyncpg
if you dont mind i can polish this PR and add missing parts

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[ArcLightSlavik]

Don't have time to add the Update method, so if anyone wants to do that I would be very happy 🙂
We do need to synchronize solutions with #2665 (async here / non async there). I've took the liberty to implement the delete method similar to https://github.com/tiangolo/full-stack-fastapi-postgresql but update would be more complex with password.

[grillazz]

Don't have time to add the Update method, so if anyone wants to do that I would be very happy 🙂
We do need to synchronize solutions with #2665 (async here / non async there). I've took the liberty to implement the delete method similar to https://github.com/tiangolo/full-stack-fastapi-postgresql but update would be more complex with password.

@ArcLightSlavik is below model method a solution for pass update for you:
@password.setter def password(self, psw):
?

[aakashnand]

@grillazz Did you tagged correct person in above comment? I am bit out of context here 😄

[grillazz]

@grillazz Did you tagged correct person in above comment? I am bit out of context here 😄

sorry my bad

[ArcLightSlavik]

@grillazz Not really, I want the main insparation taken from https://github.com/tiangolo/full-stack-fastapi-postgresql/blob/master/%7B%7Bcookiecutter.project_slug%7D%7D/backend/app/app/crud/crud_user.py#L27, but without the usage of classes.
Aka:

async def update_user(db: AsyncSession, .......................):
    .... do stuff

[jcf-dev]

The get_db dependency causes a weird
TypeError: <async_generator object get_db at 0x7ff6d9d9aa60> is not a callable object
issue on my project.

Here's my code:

db.py

from typing import Generator
from .db.session import SessionLocal

async def get_db() -> Generator:
    try:
        db = SessionLocal()
        yield db
    finally:
        await db.close()

session.py

from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from .core.config import settings

engine = create_async_engine(
    settings.SQLALCHEMY_DATABASE_URI,
    pool_pre_ping=True
)
SessionLocal = AsyncSession(
    autocommit=False,
    autoflush=False,
    bind=engine
)

[grillazz]

@joweenflores below is working well for me:

from typing import AsyncGenerator
from sqlalchemy.exc import SQLAlchemyError
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.orm import sessionmaker

from the_app import config

global_settings = config.get_settings()
url = global_settings.asyncpg_url

engine = create_async_engine(
    url,
    echo=True,
)

# expire_on_commit=False will prevent attributes from being expired
# after commit.
async_session = sessionmaker(engine, expire_on_commit=False, class_=AsyncSession)


# Dependency
async def get_db() -> AsyncGenerator:
    session = async_session()
    try:
        yield session
        await session.commit()
    except SQLAlchemyError as ex:
        await session.rollback()
        raise ex
    finally:
        await session.close()

[ArcLightSlavik]

Already in #3096 but fix was using Depends(get_db) not Depends(get_db())

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[musicinmybrain]

Currently, sqlalchemy 1.4 is not allowed by pyproject.toml. I suppose that restriction would need to be loosened as well.

[ArcLightSlavik]

@musicinmybrain That would be a separate PR, it doesn't affect end users only the tests in this project.

[Kludex]

Actually, @musicinmybrain is right.
The thing is that everything on the docs_src should be added on the tests as well, otherwise the coverage will drop.
Unfortunately, this is only true if #1904 gets merged. 😅

Well, in summary, the version needs to change. 😗

[ArcLightSlavik]

Eh fair I guess, although the sound of tests for documentation scares me 😄

[Kludex]

In the case of this PR, I guess you just need to reimport the test function, you can check my PR above or click here.

[ArcLightSlavik]

If someone could do it I would be happy, don't have time to look into it for a while 😢

[jacobhjkim]

Any updates on this PR?

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