Using Alembic API from inside application code

Question

I am using SQLite as an application file format (see here for why you would want to do this) for my PySide-based desktop application. That is, when a user uses my app, their

Answer 1

Here is a purely programmical example of howto configure and call alembic commands programmatically.

The directory setup (for easier code reading)

.                         # root dir
|- alembic/               # directory with migrations
|- tests/diy_alembic.py   # example script
|- alembic.ini            # ini file

And here is diy_alembic.py

import os
import argparse
from alembic.config import Config
from alembic import command
import inspect

def alembic_set_stamp_head(user_parameter):
    # set the paths values
    this_file_directory = os.path.dirname(os.path.abspath(inspect.stack()[0][1]))
    root_directory      = os.path.join(this_file_directory, '..')
    alembic_directory   = os.path.join(root_directory, 'alembic')
    ini_path            = os.path.join(root_directory, 'alembic.ini')

    # create Alembic config and feed it with paths
    config = Config(ini_path)
    config.set_main_option('script_location', alembic_directory)    
    config.cmd_opts = argparse.Namespace()   # arguments stub

    # If it is required to pass -x parameters to alembic
    x_arg = 'user_parameter=' + user_parameter
    if not hasattr(config.cmd_opts, 'x'):
        if x_arg is not None:
            setattr(config.cmd_opts, 'x', [])
            if isinstance(x_arg, list) or isinstance(x_arg, tuple):
                for x in x_arg:
                    config.cmd_opts.x.append(x)
            else:
                config.cmd_opts.x.append(x_arg)
        else:
            setattr(config.cmd_opts, 'x', None)

    #prepare and run the command
    revision = 'head'
    sql = False
    tag = None
    command.stamp(config, revision, sql=sql, tag=tag)

    #upgrade command
    command.upgrade(config, revision, sql=sql, tag=tag)

The code is more or less a cut from this Flask-Alembic file. It is a good place to look at other commands usage and details.

Why this solution? - It was written in a need of creating an alembic stamps, upgrades and downgrades when running automated tests.

• os.chdir(migration_directory) interfered with some tests.
• We wanted to have ONE source of database creation and manipulation. "If we crate and manage databases with alembic, alembic but not metadata.create_all() shell be used for tests too".
• Even if the code above is longer than 4 lines, alembic showed itself as a good controllable beast if driven this way.