tiangolo
Delete cascade not working in AsyncSession
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Example Code
from typing import List, Optional
import sqlalchemy as sa
from sqlmodel import Field, Relationship, SQLModel
class Address(SQLModel, table=True):
__tablename__ = 'addresses'
id: Optional[int] = Field(default=None, primary_key=True, nullable=False)
user_id: int = Field(foreign_key='users.id', nullable=False)
user: 'User' = Relationship(back_populates='addresses', sa_relationship_kwargs={'lazy':'noload'})
class User(SQLModel, table=True):
__tablename__ = 'users'
id: Optional[int] = Field(default=None, primary_key=True, nullable=False)
name: str = Field(max_length=100, nullable=False)
addresses: List['Address'] = Relationship(back_populates='user', sa_relationship_kwargs={'cascade': 'all, delete', 'lazy':'noload'})
# when doing a delete
async def remove_user(db: AsyncSession, *, id: int):
obj = await db.get(User, id)
await db.delete(obj)
await db.commit()
Description
When using lazy='noload' in the relationship arguments it loads the user object with addresses: [] so there are no addresses to apply the cascade to, you always have to selectinload or joinedload so that when deleting the object it works.
Am I misunderstanding or doing it wrong because that looks too much work just to delete an object, specially if it has too many relations.
Operating System
Linux, Windows
Operating System Details
No response
SQLModel Version
0.0.8
Python Version
3.11
Additional Context
No response
For relationship cascades to work your related entities should be loaded first
You might want to confidure on delete on your foreign keys for db-level cascades https://docs.sqlalchemy.org/en/14/core/constraints.html#sqlalchemy.schema.ForeignKey.params.ondelete
async def main():
async with engine.connect() as connection:
await connection.run_sync(SQLModel.metadata.drop_all)
await connection.run_sync(SQLModel.metadata.create_all)
await connection.commit()
# Seed the data
async with async_sessionmaker.begin() as session:
session.add(
User(
name="Doctor",
addresses=[Address(), Address()],
)
)
async with async_sessionmaker.begin() as session:
stmt = select(User).options(joinedload(User.addresses))
user = await session.scalar(stmt)
await session.delete(user)
@ThirVondukr I am aware that we need to load the relation manually but I am asking if there is another way, since usually you may have many relations it is not practical to load each of them. Also keep in mind that these children will have other children under them that need to be loaded as well to apply the cascades.
I think using the on_delete='CASCADE' seems to be the only practical option but I read that it is not a good practice to keep the logic in the database and it should be on the ORM side.
maybe you can try to add passive_deletes=True to delete children by db cascade delete natively, also it's has better performance than sqlalchemy core.
@wangxin688 thanks I didn't know about this flag, but it still won't fix the problem because you would need to add a CASCADE on the database side. I have opted to do this for my project but everywhere I read says its not best practice.
@wangxin688 thanks I didn't know about this flag, but it still won't fix the problem because you would need to add a
CASCADEon the database side. I have opted to do this for my project but everywhere I read says its not best practice.
That's true, you need define cascade action in Column level, db natively action is always a better choice for me.
This really looks a bit unexpected.
session.delete() is run asynchronously and it could load nested objects before iterating through them.
But, there is the same issue when pure SQLAlchemy is used (see in the details):
import asyncio
from typing import List
from sqlalchemy import ForeignKey, String, select
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.orm import DeclarativeBase, Mapped, Relationship, mapped_column
class Base(DeclarativeBase):
pass
class Address(Base):
__tablename__ = "addresses"
id: Mapped[int] = mapped_column(primary_key=True)
user_id: Mapped[int] = mapped_column(ForeignKey("users.id"), nullable=False)
user: Mapped["User"] = Relationship(back_populates="addresses", lazy="noload")
class User(Base):
__tablename__ = "users"
id: Mapped[int] = mapped_column(primary_key=True)
name: Mapped[str] = mapped_column(String(100), nullable=False)
addresses: Mapped[List["Address"]] = Relationship(
back_populates="user", cascade="all", lazy="noload"
)
engine = create_async_engine("sqlite+aiosqlite:///")
async def main():
async with engine.connect() as connection:
await connection.run_sync(Base.metadata.create_all)
async with AsyncSession(engine) as session:
u = User(name="user 1", addresses=[Address(), Address()])
session.add(u)
await session.commit()
async with AsyncSession(engine) as session:
res = await session.execute(select(Address))
assert len(res.all()) == 2
async with AsyncSession(engine) as session:
u = await session.get(User, 1)
# u = await session.get(User, 1, options=[selectinload(User.addresses)])
await session.delete(u)
await session.commit()
async with AsyncSession(engine) as session:
res = await session.execute(select(Address))
addresses = list(res.all())
assert len(addresses) == 0, len(addresses) # AssertionError: 2
if __name__ == "__main__":
asyncio.run(main())
