Fix DatabricksSqlHook crash on empty result with fetch_one handler#69230
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…_one handler DBAPI fetchone() returns None on an empty result set, but the hook's _make_common_data_structure only accepted Row objects or lists of them, so run() with a scalar handler crashed on empty results instead of returning None as the common.sql contract and other providers do.
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The base implementation passes the handler result through unchanged, and scalar handlers such as fetch_one_handler legitimately return None for empty result sets, so the annotation excluded a value the method already returns. Mypy's override check rejected the Databricks subclass returning None against the narrower supertype annotation.
eladkal
approved these changes
Jul 2, 2026
…esults These hooks copy the base run() implementation, so their returned result lists can also contain None once the base _make_common_data_structure annotation admits it; mypy rejected the narrower list element type.
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Fixes a
TypeErrorinDatabricksSqlHook.run()when a scalar handler is used and the query returns no rows.DBAPI
fetchone()returnsNoneon an empty result set, and common.sql'sfetch_one_handleris typed-> tuple | Noneaccordingly (it also returnsNonefor statements wherecursor.descriptionisNone). The baseDbApiHook._make_common_data_structurepassesNonethrough unchanged, andDbApiHook.run()is annotated... | None. The Databricks override, however, only acceptedRoworSequence[Row]and raisedTypeError: Expected Sequence[Row] or Row, but got <class 'NoneType'>.User-visible impact:
DatabricksSqlHook.get_first(...)— which is justrun(handler=fetch_one_handler)— crashed on any query returning no rows, where every non-overridingDbApiHook(postgres, snowflake, ...) returnsNone. With this change the Databricks hook follows the common.sql contract and passesNonethrough.(The odbc hook's override maps falsy results to
[]instead;Noneis deliberately chosen here to preservefetchonesemantics — "no row" and "empty row set" stay distinguishable — and to match the base contract.)Found while validating #39448 against a live Databricks SQL warehouse; verified there that with this change
run(..., handler=fetch_one_handler)on an empty result returnsNoneand serializes cleanly through XCom.related: #39448
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