fix: Respect existing server default in alter column DDL #733
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Alembic expects `get_column_default_string` to be implemented in order to use it for `ALTER TABLE.. ALTER COLUMN .. SET DEFAULT` DDL. In our case, this means wrapping the default value in parentheses. We implement `get_column_default_string` and have it add parentheses for use in both `CREATE TABLE` and `ALTER TABLE` DDL. Call path for alembic relying on `get_column_default_string` is here: https://github.com/sqlalchemy/alembic/blob/cd4f404358f101b2b930013c609c074baca61468/alembic/ddl/base.py#L252 https://github.com/sqlalchemy/alembic/blob/cd4f404358f101b2b930013c609c074baca61468/alembic/ddl/base.py#L315
Include `DEFAULT (default_value)` stanzas in `ALTER COLUMN` DDL to avoid removing `DEFAULT` values when changing a column's type or nullability. Fixes: googleapis#732
olavloite
previously approved these changes
Aug 18, 2025
olavloite
approved these changes
Aug 18, 2025
This was referenced Aug 18, 2025
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Include
DEFAULT (default_value)stanzas inALTER COLUMNDDL to avoid removingDEFAULTvalues when changing a column's type or nullability.Fixes: #732