The GenericModel generated json schema seems to have an issue

[zaw007]

First Check

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

Commit to Help

• I commit to help with one of those options 👆

Example Code

from typing import Generic, TypeVar

from pydantic import BaseModel
from sqlmodel import SQLModel, Field

__all__ = ['A', 'B', 'C']

SQLModelT = TypeVar('SQLModelT', bound=SQLModel)

class A(SQLModel, Generic[SQLModelT]):
    code: int
    b: SQLModelT


class B(BaseModel, Generic[SQLModelT]):
    code: int
    b: SQLModelT


class C(SQLModel):
    id: int

Description

A using a generic SQLModel subclass to create，B using a generic BaseModel subclass to create, C is simple SQLModel.

The json schema generated by A[C] cannot be displayed correctly in the FastAPI /docs, the schema for C is not displayed.

The B[C] is normal.

Operating System

Windows

Operating System Details

No response

SQLModel Version

0.0.19

Python Version

3.10.10

Additional Context

pydantic 2.7.4
FastAPI 0.111.0

[ryangalamb]

It's worse than just the json schema. The typevar isn't used for validation at all when SQLModel is the base class.

I've opened a PR to fix the issue: #1275

In the meantime, I've worked around this the same way you described: by using pydantic.BaseModel instead of SQLModel for just the generic classes.