sqlalchemy.exc.MissingGreenlet: greenlet_spawn has not been called

[bert2002]

Hi,
I am running a new application and alembic on Python 3.12 and running into the following problem.

# alembic upgrade head
Traceback (most recent call last):
  File "/usr/local/bin/alembic", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/local/lib/python3.12/site-packages/alembic/config.py", line 641, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/usr/local/lib/python3.12/site-packages/alembic/config.py", line 631, in main
    self.run_cmd(cfg, options)
  File "/usr/local/lib/python3.12/site-packages/alembic/config.py", line 608, in run_cmd
    fn(
  File "/usr/local/lib/python3.12/site-packages/alembic/command.py", line 403, in upgrade
    script.run_env()
  File "/usr/local/lib/python3.12/site-packages/alembic/script/base.py", line 583, in run_env
    util.load_python_file(self.dir, "env.py")
  File "/usr/local/lib/python3.12/site-packages/alembic/util/pyfiles.py", line 95, in load_python_file
    module = load_module_py(module_id, path)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/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 994, in exec_module
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "/app/src/alembic/env.py", line 90, in <module>
    run_migrations_online()
  File "/app/src/alembic/env.py", line 78, in run_migrations_online
    with connectable.connect() as connection:
         ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/engine/base.py", line 3268, in connect
    return self._connection_cls(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/engine/base.py", line 145, in __init__
    self._dbapi_connection = engine.raw_connection()
                             ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/engine/base.py", line 3292, in raw_connection
    return self.pool.connect()
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 452, in connect
    return _ConnectionFairy._checkout(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 1269, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 716, in checkout
    rec = pool._do_get()
          ^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/impl.py", line 284, in _do_get
    return self._create_connection()
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 393, in _create_connection
    return _ConnectionRecord(self)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 678, in __init__
    self.__connect()
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 902, in __connect
    with util.safe_reraise():
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/util/langhelpers.py", line 146, in __exit__
    raise exc_value.with_traceback(exc_tb)
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 898, in __connect
    self.dbapi_connection = connection = pool._invoke_creator(self)
                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/engine/create.py", line 637, in connect
    return dialect.connect(*cargs, **cparams)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/engine/default.py", line 616, in connect
    return self.loaded_dbapi.connect(*cargs, **cparams)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/dialects/mysql/aiomysql.py", line 264, in connect
    await_only(creator_fn(*arg, **kw)),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 116, in await_only
    raise exc.MissingGreenlet(
sqlalchemy.exc.MissingGreenlet: greenlet_spawn has not been called; can't call await_only() here. Was IO attempted in an unexpected place? (Background on this error at: https://sqlalche.me/e/20/xd2s)

The configuration looks like this:

from logging.config import fileConfig

from sqlalchemy import engine_from_config
from sqlalchemy import pool

from alembic import context

#
# ENV
#

import os
from os.path import join, dirname
from dotenv import load_dotenv
dotenv_path = join(dirname(__file__), '../.env')
load_dotenv(dotenv_path)

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
if config.config_file_name is not None:
  fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = None

# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.

# set new database uri from .env file
config.set_section_option("alembic", "sqlalchemy.url", "mysql+aiomysql://%s:%s@%s/%s" % (os.environ.get('DATABASE_USER'),os.environ.get('DATABASE_PASSWORD'),os.environ.get('DATABASE_HOST'),os.environ.get('DATABASE_DB')))

def run_migrations_offline() -> None:
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online() -> None:
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section, {}),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection, target_metadata=target_metadata
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
  run_migrations_offline()
else:
  run_migrations_online()

Its the default configuration, besides the sqlalchemy.url which gets set correctly. Any idea why this error is happening?

Thanks,
bert

[zzzeek]

hi -

you are using a driver that only supports asyncio (aiomysql). The env.py you have above is written for a synchronous driver. Use a sync driver in your alembic script, such as mysqlclient or pymysql (see https://docs.sqlalchemy.org/en/20/dialects/mysql.html#module-sqlalchemy.dialects.mysql.mysqldb).

alternately, if you want to use an async driver in your alembic script, you would need to rework the env.py script to be compatible with this, see https://alembic.sqlalchemy.org/en/latest/cookbook.html#using-asyncio-with-alembic where you can choose from a pre-established template option or modify your env.py in place.

[bert2002]

works perfectly. Thanks a lot.