.ini文件加载环境变量

Question

I am using Alembic for migrations implementation in a Flask project. There is a alembic.ini file where the database configs must be specified:

sqlalchemy.url = driver://user:password@host/dbname

Is there a way to specify the parameters from the environment variables? I've tried to load them in this way $(env_var) but with no success. Thanks!

Answer 1

I've solved the problem by setting sqlalchemy.url in env.py as @dirn suggested.

config.set_main_option('sqlalchemy.url', <db_uri>) did the trick, where <db_uri> can be loaded from environment or config file.

Answer 2

I was looking for a while how to manage this for mutli-databases

Here is what I did. I have two databases : logs and ohlc

According to the doc , I have setup the alembic like that

alembic init --template multidb

alembic.ini

databases = logs, ohlc
[logs]
sqlalchemy.url = postgresql://botcrypto:botcrypto@localhost/logs
[ohlc]
sqlalchemy.url = postgresql://botcrypto:botcrypto@localhost/ohlc

env.py

[...]
# 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.
fileConfig(config.config_file_name)
logger = logging.getLogger('alembic.env')

# overwrite alembic.ini db urls from the config file
settings_path = os.environ.get('SETTINGS')
if settings_path:
    with open(settings_path) as fd:
        settings = conf.load(fd, context=os.environ) # loads the config.yml
    config.set_section_option("ohlc", "sqlalchemy.url", settings["databases"]["ohlc"])
    config.set_section_option("logs", "sqlalchemy.url", settings["databases"]["logs"])
else:
    logger.warning('Environment variable SETTINGS missing - use default alembic.ini configuration')
[...]

config.yml

databases:
    logs: postgresql://botcrypto:botcrypto@127.0.0.1:5432/logs
    ohlc: postgresql://botcrypto:botcrypto@127.0.0.1:5432/ohlc

usage

SETTINGS=config.yml alembic upgrade head

Hope it can helps !

Answer 3

Just to add to the existing answers, the alembic tutorial has this to say:

• sqlalchemy.url - A URL to connect to the database via SQLAlchemy. This configuration value is only used if the env.py file calls upon them; in the “generic” template, the call to config.get_main_option("sqlalchemy.url") in the run_migrations_offline() function and the call to engine_from_config(prefix="sqlalchemy.") in the run_migrations_online() function are where this key is referenced. If the SQLAlchemy URL should come from some other source, such as from environment variables or a global registry, or if the migration environment makes use of multiple database URLs, the developer is encouraged to alter the env.py file to use whatever methods are appropriate in order to acquire the database URL or URLs.

Answer 4

Building on top of @dimmg's answer:
You can overwrite the sqlalchemy.url specified in alembic.ini in the env.py file.

Single Database

env.py

Insert

config.set_main_option('sqlalchemy.url', <db_uri>)

where <db_uri> can be loaded from the environment or config file.

Multi-Database

env.py

Assuming you a have multi-database setup with databases db_a and db_b , insert

config.set_section_option('db_a', 'sqlalchemy.url', <db_uri_a>)
config.set_section_option('db_b', 'sqlalchemy.url', <db_uri_b>)

where <db_uri_a> and <db_uri_b> are the database URI for db_a and db_b , respectively, and can be loaded from the environment or config file.

Note

Make sure to also indicate in the alembic.ini file that the parameters specified there are overwritten in in the env.py file. The section in which the sqlalchemy.url s are specified could even be removed entirely for all DB's for which the URI is overwritten in env.py .
This will hopefully save you or collaborators some confusion when returning to the project later.