TypeAdapter doesn't work with inheritance

[benglewis]

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 sqlmodel import SQLModel

class A(SQLModel):
  a: int

class B(A):
  b: str

from pydantic import TypeAdapter

assert TypeAdapter(A | B).validate_python({'a': 1, 'b': 's'}) == B(a=1, b='s')

Description

I have a similar but equally weird issue. I am using a Union and a TypeAdapter and somehow, using SQLModel rather than BaseModel breaks the automatic detection of which class should be chosen. The only thing that I can see that could be the cause is that class B inherits from class A.

The TypeAdapter produces A(a=1) instead of `B(a=1, b='s').

Operating System

Linux, macOS

Operating System Details

No response

SQLModel Version

0.0.22

Python Version

Python 3.12.7

Additional Context

I initially thought that this was intended/broken behavior in pydantic, spent a lot of time trying to write tests and fix their Rust code with AI helpers... only to realize that this is actually a sqlmodel bug :'(

[benglewis]

@tiangolo Should I move this to a regular Issue? I don't know if this is the right place for this given that I'm not raising something so much as pointing out a bug

[YuriiMotov]

The problem is that the first model that passes validation is being chosen as resulting.
When data is validated with model A it produces valid object (extra is ignored by default), so it just returns the instance of A.
Just swapping A and B in Union will lead to returning expected result.

Still this is different from how Pydantic models work - with Pydantic models it works regardless the order