Fix after model validator signatures

[Viicos]

Rationale for this change

(Partially?) fixes #2590.

See https://pydantic.dev/articles/pydantic-v2-12-release#after-model-validators.

Are these changes tested?

Are there any user-facing changes?

[kevinjqliu]

Thank you for the fix!

I see this is a breaking change from pydantic/pydantic#11957
I tested this locally with pydantic 2.12.2, and the tests passed

[Viicos]

I see this is a breaking change

The signature you used wasn't documented anywhere, so more a https://xkcd.com/1172/ than a breaking change. However, I came across several libraries using this signature, so I'm wondering where it came from.

[kevinjqliu]

@Viicos looks like we replaced root_validator with model_validator and retain the same syntax
https://github.com/apache/iceberg/pull/7782/files#diff-6c71fbd8a334d7330d1be4c2a431ff6293cf46a3f95984c40b740e9f2ccdd744L341-L342

this syntax is still fairly prevalent, https://github.com/search?q=%2F%40model_validator%5C%28mode%3D.*after.*%5C%29%5Cn.*def+.*%5C%28cls%2F&type=code

Thanks again for the fix!

[Viicos]

Thanks, that would explain why I had some reports using this signature then! The migration guide doesn't properly mention the allowed signatures, so I'll make sure to update it even though the impact is way lower today.

[Viicos]

this syntax is still fairly prevalent, https://github.com/search?q=%2F%40model_validator%5C%28mode%3D.*after.*%5C%29%5Cn.*def+.*%5C%28cls%2F&type=code

I also saw this, FYI we are reverting the change in the next 2.12 patch release and adding a deprecation warning instead.

[HonahX]

Thanks for the fix! I used to wonder why we not just use self in the after validator since the object is already initialized.

[Viicos]

Thanks for the fix! I used to wonder why we not just use self in the after validator since the object is already initialized.

Yes this is still the only expected way to use it. Since 2.12.3, a deprecation warning suggesting to use instance methods is emitted when using class methods.

[ForeverAngry]

@Viicos Thanks for the fix, this is working well for me. @Fokko and @kevinjqliu can we get this merged?!

[kevinjqliu]

Thanks for the fix @Viicos and thank you everyone for the review.

As a followup, I'll also take a look at other after model validators.
EDIT: looks like the other ones are all using self :)