examples.asyncio.async_orm — SQLAlchemy 2.0 Documentation

Release: 2.0.39 | Release Date: March 11, 2025

# SQLAlchemy 2.0 Documentation

# Source code for examples.asyncio.async_orm

    """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.first()

            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())