Support inferring schemas from Python dataclasses by Abacn · Pull Request #37728 · apache/beam

Abacn · 2026-02-28T19:15:04Z

Fix #22085

Tested with JdbcIO write using dataclass as input type and worked. Previously would get

  File "/Users/../beam/sdks/python/apache_beam/coders/typecoders.py", line 175, in get_coder
    return coder.from_type_hint(typehint, self)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/Users/../beam/sdks/python/apache_beam/coders/row_coder.py", line 117, in from_type_hint
    schema = schema_from_element_type(type_hint)
  File "/Users/../beam/sdks/python/apache_beam/typehints/schemas.py", line 642, in schema_from_element_type
    raise TypeError(
    ...<2 lines>...
        "https://s.apache.org/beam-python-schemas")
TypeError: Could not determine schema for type hint <class '__main__.JdbcWriteTestRow'>. Did you mean to create a schema-aware PCollection? See https://s.apache.org/beam-python-schemas

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gemini-code-assist · 2026-02-28T19:15:21Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances Apache Beam's type hinting capabilities by introducing comprehensive support for Python dataclasses. It enables the system to recognize, convert, and infer schemas from dataclasses, integrating them seamlessly into Beam's data processing model, similar to how NamedTuples are handled.

Highlights

Dataclass Recognition: A new utility function, match_is_dataclass, was added to accurately identify Python dataclass types within the type hinting system.
Type Conversion Integration: The convert_to_beam_type mechanism was updated to include dataclass recognition, allowing Beam to properly process and convert dataclass types.
RowType Constraint Generation: The RowTypeConstraint.from_user_type method was extended to correctly extract fields and their types from dataclasses, facilitating the generation of Beam schemas.
Schema Inference Update: The schema_from_element_type function was modified to infer schemas directly from dataclasses, providing consistent behavior with existing NamedTuple support.
Comprehensive Testing: New unit tests were introduced to validate the roundtrip conversion of dataclasses to Beam schemas and to ensure their correct schema inference.

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Changelog

sdks/python/apache_beam/typehints/native_type_compatibility.py
- Imported the dataclasses module.
- Added a new function match_is_dataclass to check if a type is a dataclass.
- Updated convert_to_beam_type to include a _TypeMapEntry for dataclasses.
sdks/python/apache_beam/typehints/row_type.py
- Imported match_is_dataclass from native_type_compatibility.
- Extended the from_user_type static method to handle dataclass types, extracting their fields and types to construct RowTypeConstraint instances.
sdks/python/apache_beam/typehints/schemas.py
- Imported match_is_dataclass from native_type_compatibility.
- Modified schema_from_element_type to infer schemas from dataclasses, alongside named tuples.
sdks/python/apache_beam/typehints/schemas_test.py
- Imported the dataclasses module.
- Added test_dataclass_roundtrip to verify the conversion of dataclasses to RowTypeConstraint and schema generation.
- Added test_trivial_example_dataclass to test the schema inference for a basic dataclass structure.

Activity

Addressed issue [Feature Request]: Support for inferring schemas from Python dataclasses #22085.
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github-actions · 2026-03-09T16:27:17Z

Checks are failing. Will not request review until checks are succeeding. If you'd like to override that behavior, comment assign set of reviewers

Abacn · 2026-03-09T17:21:59Z

assign set of reviewers

github-actions · 2026-03-09T17:23:13Z

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R: @claudevdm for label python.

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claudevdm

This only applies when the typehint is beam.Row right? Just want to be sure we arent changing default coders in update incompatible way.

claudevdm · 2026-03-09T17:31:53Z

/gemini review

gemini-code-assist

Code Review

This pull request adds support for inferring schemas from Python dataclasses, which is a great enhancement. The changes are logical and include good test coverage for the new functionality. I've found one area for improvement regarding code duplication, which could enhance maintainability.

sdks/python/apache_beam/typehints/row_type.py

Abacn · 2026-03-09T19:50:28Z

This only applies when the typehint is beam.Row right? Just want to be sure we arent changing default coders in update incompatible way.

Yes, the entrypoint of the change being effective is

https://github.com/apache/beam/pull/37728/changes#diff-d31b9184f7423473c4e6deda80b237aa474228143a0bab2faedd9afe2e944982R633

Previously, same config results in TypeError (shown in PR description), therefore no upgrade compatibility concern.

There was a change in native_type_compatibility.py added dataclass into type_map that might change typehint of existing dataclasses

0aa835d#diff-3f6570dbd8f6850deb466f36b7b7983e9b5c1adaec3810dfe672e108188a35ebR426

Further testing shows this change was actually dead code. Dataclass will hit this branch:

https://github.com/Abacn/beam/blob/0aa835dcb2d2b037121cb75ee6dc439f1d364ad0/sdks/python/apache_beam/typehints/native_type_compatibility.py#L393

and return before iterating over type_map. Reverted in the latest commit.

sdks/python/apache_beam/typehints/schemas_test.py

… passing through GBK

github-actions bot added the python label Feb 28, 2026

Abacn force-pushed the dataclass-schema branch 2 times, most recently from 4099aa8 to f58f026 Compare February 28, 2026 21:55

Support inferring schemas from Python dataclasses

0aa835d

Abacn force-pushed the dataclass-schema branch from f58f026 to 0aa835d Compare March 9, 2026 14:40

Abacn marked this pull request as ready for review March 9, 2026 15:20

github-actions bot added the Next Action: Reviewers label Mar 9, 2026

claudevdm requested changes Mar 9, 2026

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gemini-code-assist bot reviewed Mar 9, 2026

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sdks/python/apache_beam/typehints/row_type.py Outdated Show resolved Hide resolved

Address comments; Revert native_type_compatibility _TypeMapEntry change

bece353

Abacn force-pushed the dataclass-schema branch from d358c00 to bece353 Compare March 9, 2026 19:45

claudevdm approved these changes Mar 9, 2026

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sdks/python/apache_beam/typehints/schemas_test.py Show resolved Hide resolved

Add unit test for named tuple and dataclasses encoded by RowCoder and…

d9921bd

… passing through GBK

claudevdm approved these changes Mar 10, 2026

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Support inferring schemas from Python dataclasses#37728

Support inferring schemas from Python dataclasses#37728
Abacn wants to merge 4 commits intoapache:masterfrom
Abacn:dataclass-schema

Abacn commented Feb 28, 2026 •

edited

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Abacn commented Feb 28, 2026 •

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