🐛 Fix `alias` support for Pydantic v2 by ravishan16 · Pull Request #1577 · fastapi/sqlmodel · GitHub

Description

This PR fixes the Field(alias="...") functionality that was broken in Pydantic v2 while maintaining full backward compatibility with Pydantic v1.

Problem

In Pydantic v2, the alias parameter in SQLModel's Field function was not working correctly for validation and serialization. The issue was that Pydantic v2 requires explicit validation_alias and serialization_alias parameters, but SQLModel wasn't automatically propagating the alias value to these parameters.

Solution

Changes Made:

Enhanced Field function:
- Added validation_alias and serialization_alias parameters
- Implemented version-specific parameter handling
Automatic alias propagation:
- Modified post_init_field_info in _compat.py to automatically set validation_alias and serialization_alias from alias when not explicitly provided (Pydantic v2 only) UPD YuriiMotov: updated it to just using alias value for validation_alias and serialization_alias if they are not specified directly
Backward compatibility:
- Filter out v2-only parameters from FieldInfo in Pydantic v1
- Raise clear RuntimeError when v2 features are used with v1
- Conditional test execution based on Pydantic version
Comprehensive testing:
- Added extensive test coverage for both Pydantic v1 and v2
- Tests automatically skip v2-specific features when running with v1
- Covers all alias scenarios including edge cases

Breaking Changes
None. This is purely a bug fix with backward compatibility maintained.

Closes
Fixes #1536

This commit fixes Field(alias="...") functionality in Pydantic v2 while maintaining full backward compatibility with Pydantic v1.

The idea looks good to me!

A couple of more things:

I think it would be nice to use alias as a default value for DB column. It can then be overridden by sa_column=Column("column_name") - decided to handle it in separate PR later
We should probably test how it works with alias generators specified in model's config (is it supported? - UPD: YES) (done)

PS: @svlandeg, sorry, I only noticed you self-assigned this PR when I was about to press "Submit review".. Hope you don't mind I submitted this review)

Pydantic's validation_alias type annotation is wider (validation_alias: str | AliasPath | AliasChoices | None), but I think it's fine if we only support str for now and extend it later

I don't have a strong preference on this.

Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>

…Yurii's comment https://github.com/fastapi/sqlmodel/pull/1577/files/34d2a4500e26a62f7b9e30982eebd44538e08859\#r2392422553

Hope you don't mind I submitted this review

Of course not! I tentatively assign PRs when I want to review them in the near future, just to keep track of them, but sometimes other tasks come in between 🙈 Feel free to review whatever you want!

@YuriiMotov @svlandeg I’ve addressed all the comments from the review. Let me know if there’s anything else you’d like me to focus on.

Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>

I simplified code a bit - moved alias propagation logic to Field.__init__ so that it would be all in one place.
Also, got rid of deprecation warnings in test.

LGTM!

Implementation is not breaking. It also handles the workaround with

Field(schema_extra={"validation_alias": "field_alias"})

that people currently use.

The only use case it can break is if users use

Field(schema_extra={"validation_alias": "field_alias"})

and want to use this model with both, Pydantic V1 and V2.
It will now raise

RuntimeError("validation_alias is not supported in Pydantic v1")

for Pydantic V1.
But it's easily fixable - just remove validation_alias (now alias works with both versions, so that workaround is not needed).

To Sebastian:

Some tests are parameterized to be run with both, SQLModel and Pydantic models, to show that they behave the same way. If you don't like it, it's easy to remove it.

@ravishan16, thank you!

Could you please let me know when this PR will be merged and released?

Awesome, thank you @ravishan16! 🚀

And thanks @YuriiMotov! 🍰

This will be available in SQLModel 0.0.29, released in the next hours. 🎉

ravishan16 added 5 commits September 25, 2025 15:53

feat: Add support for Pydantic v2 aliases

785270a

fix: Skip alias tests in Pydantic v1

72e8c36

feat: Add support for Pydantic v2 aliases

15c7954

fix: Skip alias tests in Pydantic v1

3cc2b1e

fix: Add Pydantic v2 alias support with backward compatibility

34d2a45

This commit fixes Field(alias="...") functionality in Pydantic v2 while maintaining full backward compatibility with Pydantic v1.

ravishan16 marked this pull request as ready for review September 25, 2025 23:02

ravishan16 mentioned this pull request Sep 25, 2025

Field(alias="") doesn't work with Pydantic V2 #1536

Closed

1 task done

svlandeg added the bug Something isn't working label Sep 26, 2025

svlandeg self-assigned this Sep 26, 2025

YuriiMotov reviewed Sep 30, 2025

View reviewed changes

ravishan16 and others added 3 commits September 30, 2025 16:49

Apply suggestion from @YuriiMotov

6667109

Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>

fix: move this outside of if..else.. block to avoid duplicati as per …

382a52d

…Yurii's comment https://github.com/fastapi/sqlmodel/pull/1577/files/34d2a4500e26a62f7b9e30982eebd44538e08859\#r2392422553

fix: Addressed yurii's comments

d3e761e

svlandeg removed their assignment Oct 6, 2025

This comment was marked as resolved.

Sign in to view

YuriiMotov added the waiting label Oct 8, 2025

YuriiMotov mentioned this pull request Oct 8, 2025

🐛 Fix Pydantic alias bug #1379

Closed

1 task

ravishan16 and others added 5 commits October 8, 2025 17:31

Merge branch 'fastapi:main' into issue-1536-alias-pydantic-v2

e3dbf75

Update tests/test_aliases.py

e07a259

Co-authored-by: Motov Yurii <109919500+YuriiMotov@users.noreply.github.com>

🎨 [pre-commit.ci] Auto format from pre-commit.com hooks

6b7a0a1

Field: support schema_extra aliases (v2); add alias tests

322c6af

Field: support schema_extra aliases (v2); add alias tests

6b13381

This comment was marked as resolved.

Sign in to view

github-actions Bot removed the waiting label Oct 9, 2025

compat: drop redundant v2 check in post_init_field_info;

7b2bc2c

This comment was marked as resolved.

Sign in to view

YuriiMotov added 2 commits October 9, 2025 18:39

Simplify alias propagation logic for Pydantic v2

68b31d7

Fix test name and avoid deprecation warnings

9440956

YuriiMotov approved these changes Oct 9, 2025

View reviewed changes

YuriiMotov changed the title 🐛 Fix Field alias support for Pydantic v2 with backward compatibility 🐛 Fix alias support for Pydantic v2 Oct 9, 2025

svlandeg mentioned this pull request Oct 21, 2025

Expose pydantic's Field(validation_alias=...) parameter #774

Closed

tiangolo added 2 commits December 23, 2025 12:45

Merge branch 'main' into issue-1536-alias-pydantic-v2

84cd604

✅ Tweak test to use Pydantic v1 compat utils

3ba0e8e

tiangolo approved these changes Dec 23, 2025

View reviewed changes

tiangolo enabled auto-merge (squash) December 23, 2025 20:57

tiangolo merged commit 5b1d8e6 into fastapi:main Dec 23, 2025
24 checks passed

                   *,
                   default_factory: Optional[NoArgAnyCallable] = None,
                   alias: Optional[str] = None,
+                  validation_alias: Optional[str] = None,

🐛 Fix `alias` support for Pydantic v2 by ravishan16 · Pull Request #1577 · fastapi/sqlmodel · GitHub

Repository navigation

🐛 Fix alias support for Pydantic v2 - #1577

🐛 Fix alias support for Pydantic v2#1577tiangolo merged 18 commits intofastapi:mainfastapi/sqlmodel:mainfrom ravishan16:issue-1536-alias-pydantic-v2ravishan16/sqlmodel:issue-1536-alias-pydantic-v2Copy head branch name to clipboard

Conversation

ravishan16 commented Sep 25, 2025 • edited by YuriiMotov Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Description

Problem

Solution

Changes Made:

Uh oh!

YuriiMotov left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

YuriiMotov Sep 30, 2025

Choose a reason for hiding this comment

Uh oh!

ravishan16 Sep 30, 2025

Choose a reason for hiding this comment

Uh oh!

svlandeg commented Oct 1, 2025

Uh oh!

ravishan16 commented Oct 4, 2025

Uh oh!

This comment was marked as resolved.

Uh oh!

This comment was marked as resolved.

This comment was marked as resolved.

YuriiMotov commented Oct 9, 2025

Uh oh!

YuriiMotov left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

To Sebastian:

Uh oh!

xdewx commented Nov 13, 2025

Uh oh!

tiangolo left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

🐛 Fix alias support for Pydantic v2#1577
tiangolo merged 18 commits into
fastapi:mainfrom
ravishan16:issue-1536-alias-pydantic-v2

ravishan16 commented Sep 25, 2025 •
edited by YuriiMotov
Loading

YuriiMotov left a comment •
edited
Loading

YuriiMotov left a comment •
edited
Loading