sqlalchemy v2.0.36 MappedAsDataclass

[benedikt-bartscher]

sqlalchemy introduced a new check/validation which breaks sqlalchemy-history compability with MappedAsDataclass

from sqlalchemy.orm import DeclarativeBase, Mapped, MappedAsDataclass, mapped_column
from sqlalchemy_history import make_versioned

make_versioned(user_cls="")


class Base(MappedAsDataclass, DeclarativeBase):
    pass


class MyModel(Base):
    __versioned__ = {}
    __tablename__ = "my_model"
    id: Mapped[int] = mapped_column(primary_key=True)


_ = MyModel(id=1)

sqlalchemy.exc.InvalidRequestError: Class <class 'sqlalchemy_history.model_builder.MyModelVersion'> already defines a '__table__'. ORM Annotated Dataclasses do not support a pre-existing '__table__' element

upstream refs:
sqlalchemy/sqlalchemy#11973
sqlalchemy/sqlalchemy@270b46c

[AbdealiLoKo]

Hm, I havent tried MappedAsDataclass yet - do you have any experience or suggestions on how to get this to work ?
PRs are welcome !

[abulvenz]

Yes, I can confirm this.

[benedikt-bartscher]

Hm, I havent tried MappedAsDataclass yet - do you have any experience or suggestions on how to get this to work ? PRs are welcome !

Not really, i do not have looked into the sqlalchemy-history internals yet, but maybe i will in the next days

[benedikt-bartscher]

The issue is that sqlalchemy-history tries to build a versioned class based on the model base class (the class inheriting from DeclarativeBase) while using __table__ for the fields. If your base class has MappedAsDataClass it won't accept __table__ with sqlalchemy 2.0.36.

You can mitigate it like this:
before:

class Base(DeclarativeBase, MappedAsDataclass):
    pass

make_versioned(options={"base_classes": (Base)})

class YourModel(Base): ....

after:

class Base(DeclarativeBase):
    pass

class DataclassBase(Base, MappedAsDataclass):
    __abstract__ = True

make_versioned(options={"base_classes": (Base)})

class YourModel(DataclassBase): ....