async/await FastAPI with SQLAlchemy test

main.py

#!/usr/bin/env python3
"""
1. Install Python 3.7 and `pipenv`: https://docs.pipenv.org/en/latest/
2. `pipenv install`
3. `pipenv shell`
4. `./main.py`
5. In your browser, visit http://localhost:8000/parents

See comments in lines 92-108 for details on where I'm struggling.
"""

import logging
from typing import List
from pprint import pprint

import uvicorn
from databases import Database
from fastapi import FastAPI
from pydantic import BaseModel
import sqlalchemy as sa
from sqlalchemy.engine import Engine
from sqlalchemy.orm import relationship, joinedload
from sqlalchemy.orm.query import Query
from sqlalchemy.ext.declarative import declarative_base

logger = logging.getLogger()
logger.setLevel(logging.DEBUG)

AlchemyBase = declarative_base()

DATABASE_URL = "sqlite:///./test.db"
db = Database(DATABASE_URL)


"""SQLAlchemy model classes"""
class Parent(AlchemyBase):
    __tablename__ = 'parents'

    id = sa.Column(sa.Integer, primary_key=True)
    name = sa.Column(sa.String)

    children = relationship('Child', back_populates='parent')

class Child(AlchemyBase):
    __tablename__ = 'children'

    id = sa.Column(sa.Integer, primary_key=True)
    name = sa.Column(sa.String)
    parent_id = sa.Column(sa.Integer, sa.ForeignKey('parents.id'))

    parent = relationship('Parent', back_populates='children')


"""Pydantic FastAPI type classes"""
class ChildOut(BaseModel):
    id: int
    name: str

class ParentOut(BaseModel):
    id: int
    name: str
    children: List[ChildOut] = []


"""Load app and initialize database"""
app = FastAPI()

### Bootstrap the database; this is only necessary to create the tables and data for this example
# I would manage the database with migrations rather than creating an engine normally
engine: Engine = sa.create_engine(
    DATABASE_URL, connect_args={"check_same_thread": False}
)
AlchemyBase.metadata.create_all(bind=engine)
engine.execute("INSERT OR REPLACE INTO parents (id, name) VALUES (1, 'First Parent'), (2, 'Second Parent'), (3, 'Third Parent')")
engine.execute("INSERT OR REPLACE INTO children (id, name, parent_id) VALUES (1, 'Child A', 1), (2, 'Child B', 1), (3, 'Child C', 2)")
### End example bootstrapping code


"""Define app events for managing database lifecycle"""
@app.on_event("startup")
async def startup():
    await db.database.connect()

@app.on_event("shutdown")
async def shutdown():
    await db.database.disconnect()


"""Define app routes for fetching data"""
@app.get('/parents', response_model=List[ParentOut])
async def read_parents():
    query = Query(Parent).options(joinedload('children'))
    # This logic is how SQLAlchemy handles things internally; similarly, I could just do this:
    #     statement = query.with_labels().statement
    #     results = await db.fetch_all(statement)
    # Best I can tell, I'll need access to the context to correctly map stuff (hence this code)
    query_context = query._compile_context()
    query_context.statement.use_labels = True
    logger.info(f'QUERY: {query_context.statement}')
    results = await db.fetch_all(statement)
    # For logging purposes...
    results_as_dicts = [
        {column: value for column, value in rowproxy.items()} for rowproxy in results
    ]
    logger.info(f'RESULTS: {pprint(results_as_dicts)}')
    # At this point I have a query, a context, and a result set, and I need to use those things to
    # map the results into a dict that I can return (at which point Pydantic will convert the dict
    # into a list of ParentOut objects)
    return []


"""Easy server running for debugging"""
if __name__ == "__main__":
    uvicorn.run(app, host="localhost", port=8000)

Pipfile

[[source]]
name = "pypi"
url = "https://pypi.org/simple"
verify_ssl = true

[dev-packages]
pylint = "*"

[packages]
sqlalchemy = "*"
databases = {extras = ["sqlite"],version = "*"}
fastapi = "*"
uvicorn = "*"

[requires]
python_version = "3.7"

Pipfile.lock

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@onecrayon How you deal with inserts?

@Mdslino I don't; this code is an unworking fragment that illustrates something I haven't been able to get working. See https://stackoverflow.com/questions/57228874/how-to-translate-sqlalchemy-result-rows-into-nested-dicts

@onecrayon SQLAlchemy ORM is not compatible with async; you can't await orm query (only CORE queries can be awaitable)

@DennisMatveyev the objective is not to make SQLAlchemy ORM async. The Query object from the ORM package was used just to create the statement, just like a query with core package. The issue @onecrayon was trying to address is when you query a object with relationship and the relationship is not loaded as a nested dict in the results.

@onecrayon have you actually been able to load nested relationships?

Also, line 82 and 86 should probably be db.connect and db.disconnect as db is already instantiated as Database on line 32.

# link to the SQLAlchemy table behind the table class
notes = Note.__table__

async def get(id: int):
    query = notes.select().where(id == notes.c.id)
    return await database.fetch_one(query=query)

Simply that above will not fetch any nested relationships for me that the notes model would have. Still not clear on how I should get the nested relationships out yet.

@tanhaa Unfortunately, no. I have temporarily given up on this project, since the side project I was working on that needed async database connections got back-burnered for a while. I'm hoping that by the time I return to it, there will be a way to just flat-out run SQLAlchemy from async code.

@onecrayon finally we have a solution i did a bit of testing and the results are amazing

@router.post('/sync_user')
async def sync_user(login: schemas.Login, db: Session = Depends(get_db)):
    start = datetime.now()
    if user := crud.login.get_by_email(db, login.email):
        end = datetime.now()
        duration = end - start
        logger.info(f'Login Sync Duration: {duration.total_seconds()}')
        return user


@router.post('/async_user')
async def async_user(login: schemas.Login, db: Session = Depends(get_db)):
    start = datetime.now()
    if user := await async_(crud.login.get_by_email)(db, login.email):
        end = datetime.now()
        duration = end - start
        logger.info(f'Login Async Duration: {duration.total_seconds()}')
        return user

Login Sync Duration: 0.015734
Login Async Duration: 0.002904

Now sqlalchemy orm is async/await ready!

@prostomarkeloff That's awesome news! Do you have a link to information about what version this feature is available in?

1.4. It's already on master but not yet on pypi.

1.4. It's already on master but not yet on pypi.

Any news when they about to release this version?

It's done! It's on PyPI officially :)

See, https://docs.sqlalchemy.org/en/14/orm/extensions/asyncio.html
with the caveats outlined in the same page:
https://docs.sqlalchemy.org/en/14/orm/extensions/asyncio.html#preventing-implicit-io-when-using-asyncsession