SqlAlchemy asyncio orm：如何查询数据库

Question

在 SqlAlchemy 异步 orm 引擎中如何查询表并获取值或全部？

我知道我可以做的非异步方法

SESSION.query(TableClass).get(x)

但尝试使用异步方法会引发下一个错误：

AttributeError: 'AsyncSession' object has no attribute 'query'.

这是我定义的 SESSION 变量。 LOOP 变量只是 asyncio.get_event_loop() 用于在我的 sql 模块加载时启动异步方法并填充用作缓存的变量以避免每次我需要某些东西时缓存数据库：

from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, scoped_session

from .. import CONFIG, LOOP

def _build_async_db_uri(uri):
    if "+asyncpg" not in uri:
        return '+asyncpg:'.join(uri.split(":", 1))
    return uri

async def start() -> declarative_base:
    engine = create_async_engine(_build_async_db_uri(CONFIG.general.sqlalchemy_db_uri))
    async with engine.begin() as conn:
        BASE.metadata.bind = engine
        await conn.run_sync(BASE.metadata.create_all)
    return scoped_session(sessionmaker(bind=engine, autoflush=False, class_=AsyncSession))


BASE = declarative_base()
SESSION = LOOP.run_until_complete(start())

这是一个表和缓存函数的例子：

class TableClass:
    __tablename__ = "tableclass"
    id = Column(Integer, primary_key = True)
    alias = Column(Integer)

CACHE = {}
async def _load_all():
    global CACHE
    try:
        curr = await SESSION.query(TableClass).all()
        CACHE = {i.id: i.alias for i in curr}

LOOP.run_until_complete(_load_all())

Answer 1

session.query 是旧的 API。异步版本使用 select 和附带的方法。

from sqlalchemy.future import select
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import sessionmaker


engine = create_async_engine(_build_async_db_uri(CONFIG.general.sqlalchemy_db_uri))
async_session = sessionmaker(
    engine, expire_on_commit=False, class_=AsyncSession
)


CACHE = {}
async def _load_all():
    global CACHE
    try:
        async with async_session() as session:
            q = select(TableClass)
            result = await session.execute(q)
            curr = result.scalars()
            CACHE = {i.id: i.alias for i in curr}
    except:
        pass

LOOP.run_until_complete(_load_all())

您可以阅读更多关于 SqlAlchemy 异步 I/O here