nikitagrover19 opened a new pull request, #39662:
URL: https://github.com/apache/beam/pull/39662
Fixes #28162
## What
`WriteToBigQuery` with `method=FILE_LOADS` previously required an explicit
`schema`, even when the input PCollection already carried a Beam schema —
for example a PCollection produced by
`ReadFromBigQuery(..., output_type='BEAM_ROW')`, or any PCollection of
NamedTuples, dataclasses, or Beam Rows. The `STORAGE_WRITE_API` method
already auto-infers a schema in this situation; this brings `FILE_LOADS`
(both JSON and AVRO temp file formats) in line with that behavior.
## How
- Added `beam_schema_to_bq_table_schema()` in `bigquery_schema_tools.py`,
the reverse of the existing `generate_user_type_from_bq_schema()`. It
converts a Beam `schema_pb2.Schema` into a BigQuery `TableSchema` dict,
handling atomic types, logical types (`Timestamp`, `Date`, `Decimal`),
nested/repeated fields, and nullability, and raises a clear `ValueError`
for types with no BigQuery equivalent (e.g. `MapType`).
- `WriteToBigQuery.expand()`'s `FILE_LOADS` branch now tries
`schema_from_element_type(pcoll.element_type)` when `self.schema is
None`, before the existing "schema required for AVRO" check — so AVRO
loads benefit from inference too, not just JSON.
- Falls back to the prior behavior (`schema` stays `None`) when the
PCollection has no attached Beam schema (e.g. plain dicts), so this is
purely additive and non-breaking.
## Testing
- Unit tests for the schema conversion covering atomic types, timestamps,
decimals, nullable fields, repeated fields, nested records, repeated
records, and the unsupported-`MapType` error case
(`bigquery_schema_tools_test.py`).
- Integration-style tests on `WriteToBigQuery` confirming: schema
auto-inference for JSON file loads, schema auto-inference for AVRO file
loads (previously always raised `"A schema must be provided"` here),
and that plain-dict PCollections are unaffected
(`bigquery_test.py`).
- Ran the existing `TestWriteToBigQuery` test class locally to check for
regressions; all passing except one pre-existing test that requires
real GCP credentials unavailable in my local environment (unrelated to
this change).
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