0.0.39 is dropping the class_registry variable from main without warnings

[12rambau]

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Example Code

import sqlmodel.main as _sm
from sqlalchemy.orm import registry as _SARegistry
from sqlmodel import SQLModel as _SQLModel

_orig_registry = _SQLModel._sa_registry  # type: ignore[attr-defined]
_orig_class_registry = _sm.class_registry

Description

We were using the class_registry variable to deal with big query compatibility and the drop of this variable makes it impossible to move to 0.0.39. Any reason it was dropped in https://github.com/fastapi/sqlmodel/pull/1806/changes#diff-d47aa94b4399636b3bf61c282806410ca16c47e6edb13a2d3ba675f9460e7389L800 ?
Would it be possible to reintroduce it as this variable was not marked as private ?

Operating System

Linux

Operating System Details

No response

Project Version

0.0.39

Python Version

No response

Additional Context

No response

[YuriiMotov]

When I reviewed that PR I searched for class_registry in the code base, and it appeared to be unused variable.
Could you please explain in more details why your code needs this?

[apoorva-01]

The reason it got dropped as "unused" is that it genuinely was. In 0.0.38 and earlier, sqlmodel.main.class_registry was just this, sitting at module scope:

class_registry = weakref.WeakValueDictionary()  # type: ignore

Nothing else in SQLModel ever wrote to it or read from it (grep the old main.py, it appears exactly once), and it was never exported from sqlmodel/__init__.py. So it was always an empty dict that no SQLModel code touched. If your BigQuery compat code was reading _sm.class_registry expecting to find your mapped classes in there, it was getting an empty mapping the whole time.

The registry that actually holds your mapped classes by name (the one SQLAlchemy uses to resolve string relationship refs) is on the registry object, not the module:

from sqlmodel import SQLModel

SQLModel._sa_registry._class_registry
# same object as sqlmodel.main.default_registry._class_registry

That's the live {name: class} mapping. Verified on 0.0.39: define a table=True model and its name shows up there. _class_registry is technically private on the SA side but it's been stable across 1.4 and 2.0.

If instead you were only using class_registry as a convenient global weak dict of your own (filling and reading it yourself, not relying on SQLModel to populate it), then just declare your own weakref.WeakValueDictionary() in your module. Nothing in SQLModel was ever backing it, so you lose nothing by owning it.

[12rambau]

thanks a lot, we followed your advice and it's working just fine !