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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"alembic incompatibility with sqlalchemy \u003c 1.3.11 due to computed columns","articleBody":"#### Environment details\r\n\r\n  - Programming language: python\r\n  - OS: macos\r\n  - Language runtime version: 3.7.14 \r\n  - Package version: sqlalchemy-spanner 1.3.2, sqlalchemy 1.2.12, alembic 0.9.3\r\n\r\n#### Steps to reproduce\r\n\r\n  1. install any sqlalchemy version under 1.3.11\r\n  2. run any alembic migration \r\n \r\nEasy way to try this using the existing tests--in the [migration_test function](https://github.com/googleapis/python-spanner-sqlalchemy/blob/main/noxfile.py#L225) in noxfile.py, add \r\n\r\n```session.run(\"pip\", \"install\", \"sqlalchemy\u003e=1.1.13,\u003c=1.3.10\", \"--force-reinstall\")```\r\n\r\n at the beginning after the imports to force install the sqlalchemy versions with the incompatibilities. Then run the tests using `nox -s migration_test`. In `alembic upgrade head`, and the following error should occur:\r\n\r\n```\r\n\u003cremoved\u003e\r\n  File \"google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py\", line 352, in get_column_specification\r\n    if column.computed is not None:\r\n  File \"nox/migration_test/lib/python3.8/site-packages/sqlalchemy/sql/elements.py\", line 690, in __getattr__\r\n    key)\r\nAttributeError: Neither 'Column' object nor 'Comparator' object has an attribute 'computed'\r\n```\r\n\r\nThis is because the sqlalchemy_spanner alembic code [here](https://github.com/googleapis/python-spanner-sqlalchemy/blob/main/google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py#L352-L353) refers to the `computed` attribute of `Column`, which was introduced in sqlalchemy 1.3.11 ([release notes](https://github.com/sqlalchemy/sqlalchemy/releases/tag/rel_1_3_11), [code ref](https://github.com/sqlalchemy/sqlalchemy/compare/rel_1_3_10...rel_1_3_11#diff-04bfd5c1f4dc2b278cac4df823a4dca6fbb03a1c16d8dc7bb88714cf3858bce3R1347)). So, for sqlalchemy versions \u003c 1.3.11, this will throw the `AttributeError` above since `Column`s don't have the computed attribute. \r\n\r\nA simple but maybe hacky fix would be to just check if the attribute exists before accessing it:\r\n\r\nNew version\r\n```\r\nif hasattr(column, \"computed\") and column.computed is not None:\r\n    colspec += \" \" + self.process(column.computed)\r\n```\r\n\r\nOld version\r\n```\r\nif column.computed is not None:\r\n    colspec += \" \" + self.process(column.computed)\r\n```\r\n\r\nbut definitely open to suggestions for how to fix this! ","author":{"url":"https://github.com/elainearbaugh","@type":"Person","name":"elainearbaugh"},"datePublished":"2022-10-13T21:55:02.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/269/python-spanner-sqlalchemy/issues/269"}