mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-17 22:22:13 -04:00
Mike Bayer
10f05288dc
I purposely didn't spend much documentation writing about implicit IO when I first pushed out the asyncio extension because I wanted to get a sense on what kinds of issues people had. Now we know and the answer is predictably "all of them". List out all the known implicit IO points and how to avoid them. Also rename the "adapting lazy loads" section, so that the title is less suggestive that this is a necessary technique. References: #5926 Change-Id: I3933b74bd37a5b06989531adbeade34347db679b
107 lines
2.9 KiB
Python
107 lines
2.9 KiB
Python
"""Illustrates use of the sqlalchemy.ext.asyncio.AsyncSession object
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for asynchronous ORM use.
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"""
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import asyncio
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from sqlalchemy import Column
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from sqlalchemy import DateTime
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from sqlalchemy import ForeignKey
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from sqlalchemy import func
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from sqlalchemy import Integer
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from sqlalchemy import String
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from sqlalchemy.ext.asyncio import AsyncSession
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from sqlalchemy.ext.asyncio import create_async_engine
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from sqlalchemy.ext.declarative import declarative_base
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from sqlalchemy.future import select
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from sqlalchemy.orm import relationship
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from sqlalchemy.orm import selectinload
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from sqlalchemy.orm import sessionmaker
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Base = declarative_base()
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class A(Base):
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__tablename__ = "a"
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id = Column(Integer, primary_key=True)
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data = Column(String)
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create_date = Column(DateTime, server_default=func.now())
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bs = relationship("B")
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# required in order to access columns with server defaults
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# or SQL expression defaults, subsequent to a flush, without
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# triggering an expired load
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__mapper_args__ = {"eager_defaults": True}
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class B(Base):
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__tablename__ = "b"
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id = Column(Integer, primary_key=True)
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a_id = Column(ForeignKey("a.id"))
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data = Column(String)
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async def async_main():
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"""Main program function."""
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engine = create_async_engine(
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"postgresql+asyncpg://scott:tiger@localhost/test",
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echo=True,
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)
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async with engine.begin() as conn:
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await conn.run_sync(Base.metadata.drop_all)
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await conn.run_sync(Base.metadata.create_all)
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# expire_on_commit=False will prevent attributes from being expired
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# after commit.
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async_session = sessionmaker(
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engine, expire_on_commit=False, class_=AsyncSession
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)
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async with async_session() as session:
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async with session.begin():
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session.add_all(
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[
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A(bs=[B(), B()], data="a1"),
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A(bs=[B()], data="a2"),
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A(bs=[B(), B()], data="a3"),
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]
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)
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# for relationship loading, eager loading should be applied.
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stmt = select(A).options(selectinload(A.bs))
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# AsyncSession.execute() is used for 2.0 style ORM execution
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# (same as the synchronous API).
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result = await session.execute(stmt)
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# result is a buffered Result object.
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for a1 in result.scalars():
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print(a1)
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print(f"created at: {a1.create_date}")
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for b1 in a1.bs:
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print(b1)
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# for streaming ORM results, AsyncSession.stream() may be used.
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result = await session.stream(stmt)
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# result is a streaming AsyncResult object.
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async for a1 in result.scalars():
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print(a1)
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for b1 in a1.bs:
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print(b1)
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result = await session.execute(select(A).order_by(A.id))
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a1 = result.scalars().first()
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a1.data = "new data"
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await session.commit()
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asyncio.run(async_main())
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