Stack Overflow Asked by MrOldSir on January 13, 2021
I have foloving project structure
--some db:
--some db:
--alchemy:
-- __init__.py
--alembic:
-- versions
-- env.py
-- README.py
-- script.py
--migrations:
-- __init__.py
--models:
-- model_1
-- model_2
-- __init__.py
I try to autogenerate migrations by alembic.
I have Base
in __init__.py
in models folder
import sqlalchemy as sa
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base, declared_attr
metadata = sa.MetaData()
Base = declarative_base(metadata=metadata)
And import this is env.py
from logging.config import fileConfig
from alembic import context
from sqlalchemy import engine_from_config
from sqlalchemy import pool
from models import Base
config = context.config
fileConfig(config.config_file_name)
target_metadata = Base.metadata
So, when i import Base from models in env.py in alembic directory and try to generate automigration i have some error like
ModuleNotFoundError: No module named ‘models’
How i can fix this error?
The problem is that when env.py
is executed, models
is not in your PYTHONPATH
, so it can't be imported.
With the project structure you've outlined, it might be a little hard to address; the easiest solution might be to modify your PYTHONPATH
inside env.py
like this:
import sys
sys.path = ['', '..'] + sys.path[1:]
from models import Base
This will add the parent directory of alembic/
to your PYTHONPATH
so that it can find the models
module.
Alternatively, you add the directory containing your modules to your PYTHONPATH
environment variable in your shell:
$ export PYTHONPATH='/path/to/some db/some db':$PYTHONPATH
This solution is a little more brittle because you have to remember to do this each session and it will be different for each machine you intend to run Alembic on.
When I ran into this issue, the SQLAlchemy developer suggested that if I was using pip
and virtual environments, I could install my project in editable mode so that it's in the system PYTHONPATH
and Alembic would be able to find it from anywhere. More details are available in the Python packaging guide. For this, you'd need a setup.py
for your project and you may want to change your project structure so that there's a top-level module containing things like models
and alchemy
. For example:
myproj/
setup.py
alembic/
env.py
migrations/
myapp/
__init__.py
alchemy/
__init__.py
models/
__init__.py
If this is set up correctly, you can
$ pip install -e .
from inside the myproj/
directory. Then in env.py
you would then import Base
like this:
from myapp.models import Base
Correct answer by darth_mall on January 13, 2021
When a module is loaded from a file in Python, __file__
is set to its path. You can then use that with other functions to find the directory that the file is located in.
Add the following line in alembic/env.py file to resolve the ModuleNotFoundError
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
sys.path.append(BASE_DIR)
Answered by Abhishek Dhotre on January 13, 2021
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