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"""Illustrates use of the ``sqlalchemy.ext.asyncio.AsyncSession`` object
for asynchronous ORM use.
"""
from __future__ import annotations
import asyncio
import datetime
from typing import List
from typing import Optional
from sqlalchemy import ForeignKey
from sqlalchemy import func
from sqlalchemy.ext.asyncio import async_sessionmaker
from sqlalchemy.ext.asyncio import AsyncAttrs
from sqlalchemy.ext.asyncio import create_async_engine
from sqlalchemy.future import select
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column
from sqlalchemy.orm import relationship
from sqlalchemy.orm import selectinload
class Base(AsyncAttrs, DeclarativeBase):
pass
class A(Base):
__tablename__ = "a"
id: Mapped[int] = mapped_column(primary_key=True)
data: Mapped[Optional[str]]
create_date: Mapped[datetime.datetime] = mapped_column(
server_default=func.now()
)
bs: Mapped[List[B]] = relationship()
class B(Base):
__tablename__ = "b"
id: Mapped[int] = mapped_column(primary_key=True)
a_id: Mapped[int] = mapped_column(ForeignKey("a.id"))
data: Mapped[Optional[str]]
async def async_main():
"""Main program function."""
engine = create_async_engine(
"postgresql+asyncpg://scott:tiger@localhost/test",
echo=True,
)
async with engine.begin() as conn:
await conn.run_sync(Base.metadata.drop_all)
async with engine.begin() as conn:
await conn.run_sync(Base.metadata.create_all)
# expire_on_commit=False will prevent attributes from being expired
# after commit.
async_session = async_sessionmaker(engine, expire_on_commit=False)
async with async_session() as session:
async with session.begin():
session.add_all(
[
A(bs=[B(), B()], data="a1"),
A(bs=[B()], data="a2"),
A(bs=[B(), B()], data="a3"),
]
)
# for relationship loading, eager loading should be applied.
stmt = select(A).options(selectinload(A.bs))
# AsyncSession.execute() is used for 2.0 style ORM execution
# (same as the synchronous API).
result = await session.scalars(stmt)
# result is a buffered Result object.
for a1 in result:
print(a1)
print(f"created at: {a1.create_date}")
for b1 in a1.bs:
print(b1)
# for streaming ORM results, AsyncSession.stream() may be used.
result = await session.stream(stmt)
# result is a streaming AsyncResult object.
async for a1 in result.scalars():
print(a1)
for b1 in a1.bs:
print(b1)
result = await session.scalars(select(A).order_by(A.id))
a1 = result.one()
a1.data = "new data"
await session.commit()
# use the AsyncAttrs interface to accommodate for a lazy load
for b1 in await a1.awaitable_attrs.bs:
print(b1)
asyncio.run(async_main())
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