[python] add setup to BigQuery's convert row Map transform

[stankiewicz]

add setup to BigQuery's convert row Map transform

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[gemini-code-assist]

Summary of Changes

Hello @stankiewicz, 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 the StorageWriteToBigQuery transform in Apache Beam's Python SDK by optimizing how BigQuery schemas are handled during the conversion of dictionaries to Beam Rows. By introducing a dedicated setup mechanism for schema preparation, it centralizes and streamlines the process, ensuring that schemas are correctly formatted and efficiently passed to the row conversion logic. This change improves the robustness and potential performance of BigQuery write operations.

Highlights

• Schema Setup Optimization: Introduced a new nested class, ConvertToBeamRowsSetupSchema, to manage and prepare BigQuery schemas efficiently during the setup phase of the _BigQueryConvertDictToBeamRow transform.
• Integration with DoFn.SetupContextParam: Modified the beam.Map transforms within _BigQueryConvertDictToBeamRow to leverage DoFn.SetupContextParam. This ensures that the schema is processed once at setup time by ConvertToBeamRowsSetupSchema and then passed to the beam_row_from_dict function, avoiding redundant schema conversions per element.
• Consistent Schema Handling: The ConvertToBeamRowsSetupSchema now checks if the provided schema is already a bigquery.TableSchema or bigquery.TableFieldSchema and converts it using bigquery_tools.get_bq_tableschema if it's a different type, ensuring a standardized schema format for row conversion.

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[stankiewicz]

Run Python_ML PreCommit 3.13

[github-actions]

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

[stankiewicz]

failures unrelated.
tested with pytest -v --capture=no apache_beam/io/external/xlang_bigqueryio_it_test.py::BigQueryXlangStorageWriteIT::test_write_with_dicts_cdc --test-pipeline-options='--runner=TestDirectRunner ---project=xxxx

[stankiewicz]

Run Python_Dataframes PreCommit

[ahmedabu98]

Can you add some motivation behind this change?

[stankiewicz]

sure, @ahmedabu98 ,
"Convert dict to Beam Row" transform is Map per per element transform that invokes
bigquery_tools.beam_row_from_dict(element, schema).

if schema call is string or dict, it invokes conversion dict -> json string -> bigquery.TableSchema. Conversion happens for every element and it's expensive.

Change here is to add to Map transform the SetupContextParam parameter that will invoke conversion once.

Previous attempt (#36393) was reverted due to proto serialization issues.

[ahmedabu98]

Thanks, this LGTM

[github-actions]

Assigning reviewers:

R: @shunping for label python.

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