Alembic uses SQLAlchemy as the underlying engine to do change management scripts for a relational database. This is similar to Django or Rail’s migration.
When Alembic starts, it creates the Migration Environment:
myproject # your application source code
alembic/ # this directory is the home of the migration environment
env.py # this is a python script that is run whenever the alembic migration tool is called (usually connection/configuration)
README
script.py.mako # the Mako template file used to generate new migration scripts; this creates what shows up in 'versions'
alembic.ini # the 'generic' configuration file (e.g. for a single generic database configuration)
versions/ # the directory that holds the individual version scripts; ids in file names use a partial GUID approach
3512b954651e_add_account.py
2b1ae634e5cd_add_order_id.py
3adcc9a56557_rename_username_field.py
In your env.py file, you should determine when to use online mode (run against db) or offline mode (create sql)
In Alembic, you can generate migrations as SQL scripts instead of running them against the database; this is
called offline mode and called with the --sql option. You might use this when access to DDL is restricted
and SQL scripts need to be passed to someone with higher privileges.
alembic upgrade ae1027a6acf --sql
In Alembic, you can run your migrations against a database; this is called online mode.
The file that the alembic script looks for when called. This alembic.ini is a configuration file that
points you to where the database migration(s) are, what loggers you have, etc.