Alembic: alembic revision says Import Error

问题

I am trying to integrate my Flask project with Alembic
My application structure looks like

project/
       configuration/
                    __init__.py
                    dev.py
                    test.py
       core/
           # all source code
       db/
         migrations/
                    __init__.py
                    alembic.ini
                    env.py
                    versions/

When I try to run the following from my db directory, I see

 File "migration/env.py", line 55, in run_migrations_online
    from configuration import app, db
ImportError: No module named configuration

I tried the solution mentioned in Request a simple alembic working example for Auto Generating Migrations, but it does not work for me

My method in env.py run_migrations_online() with change is

def run_migrations_online():
    """Run migrations in 'online' mode.

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

    """
    import os
    import sys

    sys.path.append(os.getcwd())
    from configuration import app, db

    alembic_config = config.get_section(config.config_ini_section)
    alembic_config['sqlalchemy.url'] = app.config['SQLALCHEMY_DATABASE_URI']
    target_metadata = db.metadata

    engine = engine_from_config(
        alembic_config,
        prefix='sqlalchemy.',
        poolclass=pool.NullPool)

    connection = engine.connect()
    context.configure(
        connection=connection,
        target_metadata=target_metadata
    )

    try:
        with context.begin_transaction():
            context.run_migrations()
    finally:
        connection.close()


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

How can I fix this?

回答1:

I did export PYTHONPATH=<path_to_project> and ran the command again and it ran successfully

回答2:

You say you run something like alembic migrate --autogenerate -m 'migration description' from the directory project/db and get ImportError, right?

If so, the problem is obvious.

See: you try to import configuration module and it results in errors. Then you put sys.path.append(os.getcwd()) - in other words, you add current directory to the system path. But what is the current directory? It's project/db, and it doesn't have configuration module under it, so you continue getting ImportError.

Solution is to add to system path parent directory - project, which contains configuration module. Like so:

parent_dir = os.path.abspath(os.path.join(os.getcwd(), ".."))
sys.path.append(parent_dir)

回答3:

We've run into the same problem, it boils down to env.py not being called by revision unless the --autogenerate flag is set. You can test this by putting a print statement at the top of your env.py file.

We're working around it by calling with --autogenerate then removing the generated code.

来源：https://stackoverflow.com/questions/15648284/alembic-alembic-revision-says-import-error

标签

python

Flask

flask-sqlalchemy

alembic