add configurable write_mode to BigQueryIOManager #32998
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Added support for truncate, replace, and append modes to allow schema evolution and append-only workflows. Includes unit tests and documentation updates.
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Summary & Motivation
Added a configurable write_mode option to BigQueryIOManager to support schema evolution and different writing strategies for non-partitioned tables.
Currently, the IO manager forces a TRUNCATE operation, which deletes rows but preserves the schema. This causes failures when the DataFrame schema changes (e.g., adding/removing columns).
How I Tested These Changes
Unit Testing: Created a new test file dagster_gcp_tests/bigquery_tests/test_bigquery_write_modes.py using unittest.mock.
Verified that write_mode="truncate" triggers a TRUNCATE TABLE query.
Verified that write_mode="replace" triggers a DROP TABLE IF EXISTS query.
Verified that write_mode="append" triggers no cleanup query.
Verified that partitioned tables ignore the write mode and use the legacy DELETE FROM logic.
Added a factory test to ensure the BigQueryClient is initialized with the correct default write_mode for backward compatibility.
Changelog
feat(gcp): Add write_mode configuration to BigQueryIOManager (supports truncate, replace, append) to allow schema evolution and append-only workflows.