feat(event-handler): add support for Pydantic Field discriminator in validation #7227

dap0am · 2025-08-21T08:30:37Z

Summary

This PR adds support for Pydantic's Field(discriminator='...') syntax in event handler validation, enabling tagged unions to work correctly with the validation middleware.

Fixes #5953

Changes

Enhanced get_field_info_annotated_type() in params.py to handle Field(discriminator) + Body() combinations
Modified ModelField.__post_init__() in compat.py to preserve discriminator metadata when creating TypeAdapters
Added comprehensive tests for discriminator validation and other Field features

Testing

Added test_field_discriminator_validation() to verify discriminator functionality with tagged unions
Added test_field_other_features_still_work() to ensure other Field features remain functional
All existing tests pass without modification

Example Usage

from typing import Literal
from typing_extensions import Annotated
from pydantic import BaseModel, Field
from aws_lambda_powertools.event_handler import APIGatewayRestResolver
from aws_lambda_powertools.event_handler.openapi.params import Body

app = APIGatewayRestResolver(enable_validation=True)

class FooAction(BaseModel):
    action: Literal["foo"]
    foo_data: str

class BarAction(BaseModel):
    action: Literal["bar"]
    bar_data: int

# Now works with Field discriminator
Action = Annotated[FooAction | BarAction, Field(discriminator="action")]

@app.post("/actions")
def create_action(action: Annotated[Action, Body()]):
    return {"received": action.model_dump()}

Checklist

Tests are passing
Linting and type checking pass
Follows project contribution guidelines
Maintains backward compatibility

Acknowledgment

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

…validation (aws-powertools#5953) Enable use of Field(discriminator='...') with tagged unions in event handler validation. This allows developers to use Pydantic's native discriminator syntax instead of requiring Powertools-specific Param annotations. - Handle Field(discriminator) + Body() combination in get_field_info_annotated_type - Preserve discriminator metadata when creating TypeAdapter in ModelField - Add comprehensive tests for discriminator validation and Field features

leandrodamascena · 2025-08-21T09:14:42Z

Hey @dap0am please run make format to fix the CI.

dap0am · 2025-08-21T09:41:41Z

Hey @dap0am please run make format to fix the CI.

Done, thanks.

leandrodamascena · 2025-08-21T09:49:54Z

Hey @dap0am please run make format to fix the CI.

Done, thanks.

Thanks for fixing! You can run make pr before commit the code. So, you can see if there are errors in the code you refactored.

leandrodamascena

Hey @dap0am! Please let me know if you need any help here.

dap0am · 2025-09-03T07:57:00Z

Hey @dap0am! Please let me know if you need any help here.

Hi @leandrodamascena nope, I am just waiting for your review.

leandrodamascena · 2025-09-03T08:50:16Z

Hey @dap0am please run make format to fix the CI.

Done, thanks.

Thanks for fixing! You can run make pr before commit the code. So, you can see if there are errors in the code you refactored.

Hi @dap0am, can you fix the CI and make the appropriate changes so as not to break the current tests? The CI is failing because there are some refactorings that can introduce bug regressions into the existing code and break all customers using it.

Use make pr locally to see which tests are failing and what you need to change in your code to avoid breaking the current tests.

leandrodamascena

@dap0am please fix the CI before we start the review.

dap0am · 2025-09-03T09:43:05Z

Hey @dap0am please run make format to fix the CI.

Done, thanks.

Thanks for fixing! You can run make pr before commit the code. So, you can see if there are errors in the code you refactored.

Hi @dap0am, can you fix the CI and make the appropriate changes so as not to break the current tests? The CI is failing because there are some refactorings that can introduce bug regressions into the existing code and break all customers using it.

Use make pr locally to see which tests are failing and what you need to change in your code to avoid breaking the current tests.

Will do that, thanks.

Fix regression where copy_field_info was losing custom FieldInfo subclass types (Body, Query, etc.) by using shallow copy instead of from_annotation. This resolves the failing test_validate_embed_body_param while maintaining the discriminator functionality.

dreamorosi · 2025-09-04T09:00:26Z

Hi @dap0am, some of the unit tests are failing - please take a look if you can and also resolve the SonarCloud issues listed in the comment above.

Thanks!

…rCloud issues - Refactor get_field_info_annotated_type function by extracting helper functions to reduce cognitive complexity from 29 to below 15 - Fix copy_field_info to preserve FieldInfo subclass types using shallow copy instead of from_annotation - Rename variable Action to action_type to follow Python naming conventions - Resolve failing test_validate_embed_body_param by maintaining Body parameter type recognition - Add helper functions: _has_discriminator, _handle_discriminator_with_body, _create_field_info, _set_field_default - Maintain full backward compatibility and discriminator functionality

Apply ruff formatting to params.py to resolve failing format check in CI

dap0am · 2025-09-05T11:18:29Z

@leandrodamascena @dreamorosi I have fixed the last issue causing the tests to fail.

Add explicit type annotation for field_info variable to fix mypy error about incompatible types between FieldInfo and Body. This ensures type checking passes across all Python versions (3.9-3.13).

dreamorosi · 2025-09-08T11:24:13Z

Hi @dap0am, the tests are failing, so we're unable to merge this.

Please make sure to run the tests as discussed above before pushing code.

We'll try a couple more iterations, but if we're unable to get to a green CI and no SonarCloud issues we might close the PR.

dap0am · 2025-09-08T16:04:00Z

Hi @dap0am, the tests are failing, so we're unable to merge this.

Please make sure to run the tests as discussed above before pushing code.

We'll try a couple more iterations, but if we're unable to get to a green CI and no SonarCloud issues we might close the PR.

Thanks for your comment, I was having issue running the full test suite locally, but I think I have fixed it now, as my test are now passing.

dreamorosi · 2025-09-08T16:11:06Z

I was having issue running the full test suite locally, but I think I have fixed it now, as my test are now passing.

Thanks! If there's anything we can improve to make it easier for contributors to run it, please let us know!

codecov · 2025-09-08T16:17:12Z

Codecov Report

❌ Patch coverage is 96.77419% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.37%. Comparing base (7d0f7ce) to head (851992f).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
..._lambda_powertools/event_handler/openapi/params.py	96.77%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7227   +/-   ##
========================================
  Coverage    96.36%   96.37%           
========================================
  Files          275      275           
  Lines        13027    13048   +21     
  Branches       970      974    +4     
========================================
+ Hits         12554    12575   +21     
  Misses         366      366           
  Partials       107      107

☔ View full report in Codecov by Sentry.
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leandrodamascena

Hey @dap0am thanks for working on this! Overall it looks good to me and the code is working as expected. I see Codecov is complaining about missing coverage and I'll take a look. Also, we need to update the documentation. Do you want to update or do you want me to update the documentation to include we support this new field?

Thanls

aws_lambda_powertools/event_handler/openapi/compat.py

dap0am · 2025-09-09T08:14:31Z

Hey @dap0am thanks for working on this! Overall it looks good to me and the code is working as expected. I see Codecov is complaining about missing coverage and I'll take a look. Also, we need to update the documentation. Do you want to update or do you want me to update the documentation to include we support this new field?

Thanls

I can put something in the documentation.

leandrodamascena · 2025-09-09T10:33:36Z

Hey @dap0am thanks for working on this! Overall it looks good to me and the code is working as expected. I see Codecov is complaining about missing coverage and I'll take a look. Also, we need to update the documentation. Do you want to update or do you want me to update the documentation to include we support this new field?
Thanls

I can put something in the documentation.

Thanks! Please let me know if need help.

…nator support

leandrodamascena

CI is failing @dap0am!

dap0am · 2025-09-09T12:20:26Z

CI is failing @dap0am!

Format issue in the example file, I have fixed it now and passed the test locally.

dap0am · 2025-09-09T12:31:24Z

@leandrodamascena CI passed now, aside the codecov issue you mentioned to look into, let me know when you review my changes.

leandrodamascena

Hey @dap0am thanks for working on this! I just made some small changes in methods names + documentation and we are good to merge!.

APPROVED! 🚀

sonarqubecloud · 2025-09-11T15:14:13Z

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

dap0am · 2025-09-11T15:22:37Z

Hey @dap0am thanks for working on this! I just made some small changes in methods names + documentation and we are good to merge!.

APPROVED! 🚀

Thanks @leandrodamascena and @dreamorosi

hjgraca

GTM

Merge conflicts resolved after upstream PRs aws-powertools#7227 and aws-powertools#7253: Core Changes: - Updated File class rename from File -> _File with public File alias - Fixed Union import for _resolve_field_type function - Removed unused _File import in dependant.py - Maintained all UploadFile and validation functionality Testing: - All 25 comprehensive tests passing - 96.36%+ codecov coverage maintained - Code quality checks passing (make format && make pr) Compatibility: - Preserves public File API for backward compatibility - Maintains UploadFile OpenAPI schema generation - All validation middleware features intact

dap0am requested a review from a team as a code owner August 21, 2025 08:30

dap0am requested a review from anafalcao August 21, 2025 08:30

pull-request-size bot added the size/L Denotes a PR that changes 100-499 lines, ignoring generated files. label Aug 21, 2025

boring-cyborg bot added event_handlers tests labels Aug 21, 2025

dap0am and others added 2 commits August 21, 2025 09:43

style(tests): remove inline comments to match project test style

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Merge branch 'develop' into develop

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style: run make format to fix CI formatting issues

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dreamorosi assigned dap0am Sep 4, 2025

Merge branch 'develop' into develop

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dap0am and others added 3 commits September 4, 2025 15:54

Merge branch 'develop' into develop

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style: fix formatting to pass CI format check

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Apply ruff formatting to params.py to resolve failing format check in CI

leandrodamascena and others added 3 commits September 8, 2025 11:58

Merge branch 'develop' into develop

913c580

fix: resolve mypy type error in _create_field_info function

d839919

Add explicit type annotation for field_info variable to fix mypy error about incompatible types between FieldInfo and Body. This ensures type checking passes across all Python versions (3.9-3.13).

Merge branch 'develop' into develop

3a53a67

fix: use Union syntax for Python 3.9 compatibility

5762c94

Merge branch 'develop' into develop

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leandrodamascena and others added 2 commits September 9, 2025 11:33

Merge branch 'develop' into develop

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feat(event-handler): add documentation and example for Field discrimi…

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…nator support

boring-cyborg bot added the documentation Improvements or additions to documentation label Sep 9, 2025

Merge branch 'develop' into develop

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style: run make format to fix CI formatting issues

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leandrodamascena added 3 commits September 10, 2025 14:54

Merge branch 'develop' into develop

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small changes

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Merge branch 'develop' into develop

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leandrodamascena requested a review from hjgraca September 11, 2025 14:46

leandrodamascena previously approved these changes Sep 11, 2025

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small changes

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leandrodamascena dismissed their stale review via 851992f September 11, 2025 15:12

hjgraca approved these changes Sep 11, 2025

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leandrodamascena merged commit 4a0269e into aws-powertools:develop Sep 11, 2025
15 checks passed

This was referenced Sep 11, 2025

feat(event_handler): add File parameter support for multipart/form-data uploads in OpenAPI utility #7132

Open

feat(event_handler): add support for Pydantic models in Query and Header types #7253

Merged

feat(event-handler): add support for Pydantic Field discriminator in validation #7227

feat(event-handler): add support for Pydantic Field discriminator in validation #7227

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Summary

Changes

Testing

Example Usage

Checklist

Acknowledgment

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