`NameError: name 'FetchedValue' is not defined`

[khteh]

Describe the bug

pipenv run alembic upgrade head hit a NameError

Expected behavior

To Reproduce
Please try to provide a Minimal, Complete, and Verifiable example, with the migration script and/or the SQLAlchemy tables or models involved.
See also Reporting Bugs on the website.

    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        default=sa.func.now(),
        server_default=sa.FetchedValue()
    )

Error

$ pipenv run alembic upgrade head
Loading .env environment variables...
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade  -> ca93a9d04c54, Initial migration
Traceback (most recent call last):
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/bin/alembic", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/config.py", line 636, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/config.py", line 626, in main
    self.run_cmd(cfg, options)
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/config.py", line 603, in run_cmd
    fn(
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/command.py", line 408, in upgrade
    script.run_env()
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/script/base.py", line 586, in run_env
    util.load_python_file(self.dir, "env.py")
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/util/pyfiles.py", line 95, in load_python_file
    module = load_module_py(module_id, path)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/util/pyfiles.py", line 113, in load_module_py
    spec.loader.exec_module(module)  # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap_external>", line 995, in exec_module
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "/usr/src/Python/PythonRestAPI/migrations/env.py", line 92, in <module>
    run_migrations_online()
  File "/usr/src/Python/PythonRestAPI/migrations/env.py", line 86, in run_migrations_online
    context.run_migrations()
  File "<string>", line 8, in run_migrations
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/runtime/environment.py", line 946, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/home/khteh/.local/share/virtualenvs/PythonRestAPI-6TwrpjXm/lib/python3.12/site-packages/alembic/runtime/migration.py", line 623, in run_migrations
    step.migration_fn(**kw)
  File "/usr/src/Python/PythonRestAPI/migrations/versions/ca93a9d04c54_initial_migration.py", line 30, in upgrade
    sa.Column('created_at', sa.DateTime(timezone=True), server_default=FetchedValue(), nullable=False),
                                                                       ^^^^^^^^^^^^
NameError: name 'FetchedValue' is not defined

Versions.

• OS: Ubuntu 24.10
• Python: 3.12.7
• Alembic: 1.15.1
• SQLAlchemy: 2.0.39
• Database: PostgreSQL
• DBAPI:

Additional context

Have a nice day!

[khteh]

Solution is to add from sqlalchemy import FetchedValue to the generated script

[CaselIT]

@zzzeek I'm not sure if this is considered something the user needs to adapt or it it's generally a bug?

[zzzeek]

looks like a bug, FetchedValue we would hope is preceded by sa.