SQLAlchemy version 1.4.36 breaks SQLModel relationships

[archydeberker]

First Check

• [X] I added a very descriptive title to this issue.
• [X] I used the GitHub search to find a similar issue and didn't find it.
• [X] I searched the SQLModel documentation, with the integrated search.
• [X] I already searched in Google "How to X in SQLModel" and didn't find any information.
• [X] I already read and followed all the tutorial in the docs and didn't find an answer.
• [X] I already checked if it is not related to SQLModel but to Pydantic.
• [X] I already checked if it is not related to SQLModel but to SQLAlchemy.

👆 Not quite true - this is definitely related to SQLAlchemy!

Commit to Help

• [X] I commit to help with one of those options 👆

Example Code

from typing import Optional

from sqlmodel import Field, Relationship, SQLModel


class City(SQLModel, table=True):
    name: str = Field(primary_key=True)
    heroes: "Hero" = Relationship(back_populates="city")

class Hero(SQLModel, table=True):
    name: str = Field(primary_key=True)
    city_name: Optional[str] = Field(default=None,foreign_key="city.name")
    city: Optional[City] = Relationship(back_populates="heroes",
                              sa_relationship_kwargs=dict(cascade="all,delete")
                              )


if __name__ == "__main__":

    gotham = City(name="Gotham")
    batman = Hero(name="Batman", city=gotham)

    assert batman.name == 'Batman' # This is fine
    assert batman.city == gotham # This now breaks

Description

Our CI suddenly started failing, despite local SQLModel working fine. The issues turns out to be the transitive dependency on SQLAlchemy, which is weakly pinned: Github Actions pulled the latest version (1.4.36) and most of our tests started failing.

https://github.com/sqlalchemy/sqlalchemy/releases/tag/rel_1_4_36

The problem seems to be related to how relationships are defined, but I haven't yet dug into the SQLAlchemy changes enough to understand why that is.

I'm opening this issue chiefly to help anybody else who is confused by why suddenly their tests are failing. I'm happy to help fix it if it's affecting others too.

For the time being we have just pinned SQLAlchemy==1.4.34 in our requirements.txt.

Operating System

Linux, macOS

Operating System Details

Replicated locally and on Github Actions, both running in Docker

SQLModel Version

0.0.6

Python Version

3.9.10

Additional Context

We were previously running SQLAlchemy 1.4.34 locally and that works fine. Pinning to 1.4.36 breaks SQLModel.

[antont]

We pinned to 1.4.35, in our fork of sqlmodel. Happened to have that locally as upgraded recently and hadn't had problems. Ran into this same this afternoon. Thanks for reporting!

[JLHasson]

Same issue here, pinning to 1.4.35 resolved

[byrman]

It seems related to this recent change:

class DeclarativeMeta(
    _DynamicAttributesType, inspection.Inspectable["Mapper[Any]"]
):
    metadata: MetaData
    registry: "RegistryType"

    def __init__(
        cls, classname: Any, bases: Any, dict_: Any, **kw: Any
    ) -> None:
        # use cls.__dict__, which can be modified by an
        # __init_subclass__() method (#7900)
        dict_ = cls.__dict__  # This line is the culprit?!

https://github.com/sqlalchemy/sqlalchemy/blob/main/lib/sqlalchemy/orm/decl_api.py#L114

[jossefaz]

As @byrman wrote, the change of DeclarativeMeta seems to be the breaking change here.

[orm] [declarative] [bug] Modified the DeclarativeMeta metaclass to pass cls.dict into the declarative scanning process to look for attributes, rather than the separate dictionary passed to the type’s init() method. This allows user-defined base classes that add attributes within an init_subclass() to work as expected, as init_subclass() can only affect the cls.dict itself and not the other dictionary. This is technically a regression from 1.3 where dict was being used.

[byrman]

Not sure if this is a sustainable fix, I don't know how to leverage __init_subclass__, but adding 1 line after here makes things work again:

...
dict_used[rel_name] = rel_value
setattr(cls, rel_name, rel_value)  # Quick fix?

[jossefaz]

The SQLAlchemy maintainers confirmed that this is the issue, and also suggested a fix : https://github.com/sqlalchemy/sqlalchemy/discussions/7972#discussioncomment-2655517

[byrman]

The fix I suggested is backwards compatible. Shall I make a pull request or is there more to it than setting rel_name on the cls?

[byrman]

Let me know if this can be improved upon: https://github.com/tiangolo/sqlmodel/pull/322.

[maresb]

For reference, the actual error message is:

AttributeError: 'SomeModelWithRelationshipAttribute' object has no attribute 'the_relationship_attribute'

[eddywee]

thank you @archydeberker !! after hours of debugging i found this issue pinned the version and it works now! <3 thank you!

[GuiGarnier]

#322 fix the issue for my use cases. Thanks @byrman

[cuamckuu]

I need to downgrade SQLalchemy in requirements.txt to SQLAlchemy==1.4.35 to make relationships work

[AlanSBPerkins]

The issue remains with SQLAlchemy version 1.4.37

[Hultner]

I also ran into this issue, I have another dependency which requires SQLAlchemy > 1.4.36 which makes this quite cumbersome for me. Luckily it's just a side project which I'm using to evaluate viability of using SQLModel to reduce duplication.

[cisaacstern]

Echoing that we are also seeing this issue in our project. Pinning to sqlalchemy==1.4.35 fixes the problem. All SQLAlchemy versions > 1.4.35 break relationships. @andersy005, I'll make a note on our repo to follow this issue, and release the hard SQLAlchemy pin after this is resolved upstream.

[tiangolo]

Thanks for the report @archydeberker! :nerd_face:

And thanks for the discussion everyone! This was solved by @byrman in https://github.com/tiangolo/sqlmodel/pull/322.

It will be available in the next version, SQLModel 0.0.7, released in the next hours. :rocket:

[github-actions[bot]]

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.

[mathieu-lemay]

I can still reproduce the issue with SQLModel==0.0.8 and SQLAlchemy==1.4.41

from sqlalchemy import ForeignKeyConstraint
from sqlalchemy.orm import RelationshipProperty, selectinload
from sqlmodel import Field, Relationship, SQLModel, select


class Parent(SQLModel, table=True):
    __tablename__ = "parents"

    # The keys are set up this way
    parent_id: int = Field(primary_key=True)
    name: str

    children: list["Child"] = Relationship(
        sa_relationship=RelationshipProperty(
            "Child",
            back_populates="parent",
        )
    )


class Child(SQLModel, table=True):
    __tablename__ = "children"
    __table_args__ = (
        ForeignKeyConstraint(
            ["parent_id"],
            [f"{Parent.__tablename__}.parent_id"],
            ondelete="CASCADE",
        ),
    )

    child_id: int = Field(primary_key=True)
    parent_id: int
    name: str

    parent: Parent = Relationship(
        sa_relationship=RelationshipProperty(
            "Parent",
            cascade="all, delete",
            back_populates="children",
        )
    )


stmt = select(Parent).options(selectinload(Parent.children))

Running it gives the following error:

Traceback (most recent call last):
  File "/home/mathieu/sqlmodelbug/main2.py", line 46, in <module>
    stmt = select(Parent).options(selectinload(Parent.children))
AttributeError: type object 'Parent' has no attribute 'children'

It works fine with SLQAlchemy==1.4.35

[byrman]

Indeed, if sa_relationship is defined, my naive fix is left untouched due to these lines:

            for rel_name, rel_info in cls.__sqlmodel_relationships__.items():
                if rel_info.sa_relationship:
                    # There's a SQLAlchemy relationship declared, that takes precedence
                    # over anything else, use that and continue with the next attribute
                    dict_used[rel_name] = rel_info.sa_relationship
                    continue  # Will not reach fix!

Sorry I missed that path! It needs to be addressed, of course, but perhaps you can use this as a workaround:

class Parent(SQLModel, table=True):
    children: list["Child"] = Relationship(back_populates="parent")

class Child(SQLModel, table=True):
    parent: Parent = Relationship(back_populates="children")

[byrman]

@mathieu-lemay, I made a pull request that covers your case as well: https://github.com/tiangolo/sqlmodel/pull/461. I still have to add a test though.

[mathieu-lemay]

@byrman The workaround works so I'm gonna use that. Thanks for the fix!