Simple sample:

from sqlalchemy import Column, Integer, Computed, update, insert, select
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from sqlalchemy.orm import DeclarativeBase, declared_attr


engine = create_async_engine(url="postgresql+asyncpg://db_user:db_pass@localhost:54320/db_name")
async_session = async_sessionmaker(bind=engine)


class BaseTable(DeclarativeBase):
    @declared_attr
    def __tablename__(cls) -> str:
        return cls.__name__.lower()


class Tablichka(BaseTable):
    id = Column(Integer, primary_key=True, nullable=False, autoincrement=True)
    quantity = Column(Integer, nullable=False)
    price = Column(Integer, nullable=False)
    total_cost = Column(Integer, Computed("quantity * price"))  # Attention!

I want to update the row using an orm query. I need to get a result, so I use returning:

async def run():
    async with async_session() as session:
        statement = insert(Tablichka).values(quantity=2, price=100).returning(Tablichka)
        obj = (await session.execute(statement)).scalar_one()
        print(f"total_cost: wait 200, really {obj.total_cost}")  # total_cost: wait 200, really 200
        id = obj.id

        statement = update(Tablichka).filter_by(id=id).values(quantity=4, price=100).returning(Tablichka)
        obj = (await session.execute(statement)).scalar_one()
        print(f"total_cost: wait 400, really {obj.total_cost}")   # total_cost: wait 400, really 200

        statement = select(Tablichka).filter_by(id=id)
        obj = (await session.execute(statement)).scalar_one()
        print(f"total_cost: wait 400, really {obj.total_cost}")   # total_cost: wait 400, really 200

        await session.commit()

    async with async_session() as session:
        statement = select(Tablichka).filter_by(id=id)
        obj = (await session.execute(statement)).scalar_one()
        print(f"ntotal_cost: wait 400, really {obj.total_cost}")  # total_cost: wait 400, really 400


if __name__ == "__main__":
    import asyncio

    loop = asyncio.get_event_loop()
    loop.run_until_complete(run())
    loop.close()

After the update, I expect to get a recalculated total_cost, but I get an old total_cost. I get updated fields except calculated fields. At the same time, the value is recalculated in the database. This confirms the select query in the new session.
How do I solve the problem?

Actually, I have a working example. But I don’t have an understanding of why it works:

async def run_create(session: AsyncSession):
    statement = insert(Tablichka).values(quantity=2, price=100).returning(Tablichka)
    obj = (await session.execute(statement)).scalar_one()
    print(f"total_cost: wait 200, really {obj.total_cost}")  # total_cost: wait 200, really 200
    return obj.id


async def run_update(session: AsyncSession, id: int):
    statement = update(Tablichka).filter_by(id=id).values(quantity=4, price=100).returning(Tablichka)
    obj = (await session.execute(statement)).scalar_one()
    print(f"total_cost: wait 400, really {obj.total_cost}")  # total_cost: wait 400, really 400


async def run():
    async with async_session() as session:
        id = await run_create(session)
        await run_update(session, id)


if __name__ == "__main__":
    import asyncio

    loop = asyncio.get_event_loop()
    loop.run_until_complete(run())
    loop.close()

But in my project there is a more complex example in which I cannot use my working example. I need to fix my broken example.
I use the following versions:

python = "^3.10"
sqlalchemy = "^2.0.35"
asyncpg = "^0.29.0"
greenlet = "^3.1.0"