python Sqlalchemy不返回Map对象上带有“session.scalars”的模型对象

kzmpq1sx 于 2023-01-16 发布在 Python

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from attrs import define
from sqlalchemy.orm import (
    registry,
)
from sqlalchemy.sql import (
    schema,
    sqltypes,
)

@define(slots=False)
class Cat():
    id: int
    name: str

mapper_registry = registry()

cat_table = schema.Table(
    "cat",
    mapper_registry.metadata,
    schema.Column("id", sqltypes.Integer, primary_key=True),
    schema.Column("name", sqltypes.String, nullable=False),
)

mapper_registry.map_imperatively(models.Cat, cat_table)

async def main() -> None:
    ...
    model = Cat(1, "Meow")

    async with session_maker() as session:
        await session.add(model)  # Ok
        await session.commit()

        result = await session.scalar(cat_table.select())
        print(result)  # 1
        print(type(result))  # int

session.scalar返回int，而不是Cat
它看起来像它与查询：https://github.com/cosmicpython/code/blob/master/src/allocation/adapters/repository.py#L48
我尝试通过scalars获取对象，但需要自己构造
我做错什么了吗？还是就应该这样？

python

来源：https://stackoverflow.com/questions/75125236/sqlalchemy-does-not-return-an-model-object-with-session-scalars-on-mapped-obje

1条答案

按热度按时间

3qpi33ja1#

我认为你想要：

result = (await session.scalar(select(Cat)))
# OR
result = (await session.scalars(select(Cat))).first()

其他一些例子：

async def main() -> None:
    async_engine = create_async_engine(f"postgresql+asyncpg://{username}:{password}@/{db}", echo=False)
    async with async_engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    async_session = sessionmaker(async_engine, expire_on_commit=False, class_=AsyncSession)

    async with async_session() as session:
        cat_id = 1
        cat_name = "Meow"
        model = Cat(cat_id, cat_name)
        session.add(model)  # Ok
        await session.commit()

        def check(res, exp):
            assert res == exp
            print (res)

        result = await session.scalar(cat_table.select())
        check(result, 1)
        result = (await session.execute(cat_table.select())).first()
        check(result, (cat_id, cat_name))
        result = (await session.execute(select(cat_table))).first()
        check(result, (cat_id, cat_name))
        result = (await session.scalars(select(Cat))).first()
        check(result, model)
        result = (await session.scalar(select(Cat)))
        check(result, model)
        result = (await session.execute(select(Cat))).scalars().first()
        check(result, model)
        result = (await session.execute(select(Cat))).first()
        check(result, (model,))
        result = (await session.execute(select(Cat))).all()
        check(result, [(model,)])
        result = (await session.scalars(select(Cat))).all()
        check(result, [model])

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python Sqlalchemy不返回Map对象上带有“session.scalars”的模型对象

1条答案

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