Data migration

Ptah migration based on alembic package. Ptah adds per package migration. Migration is not required alembic environment.

Create package migration

You can use alembic operations for ddl manipulation. Here are the steps for ptah migrations generation.

• Create directory in your package that will contain migration steps.

For example:

$ cd ptah_minicms
$ mkdir migrations

So directory listing should look like this:

$ ls -l
drwxrwxr-x 2 fafhrd fafhrd 4096 2012-01-11 15:58 migrations
drwxrwxr-x 2 fafhrd fafhrd 4096 2011-12-16 11:33 static
drwxrwxr-x 2 fafhrd fafhrd 4096 2011-12-29 14:50 templates
-rw-rw-r-- 1 fafhrd fafhrd 1457 2011-12-29 14:50 actions.py
...

• Register package migrations with ptah.register_migration() api.

import ptah

ptah.register_migration(
    'ptah_minicms', 'ptah_minicms:migrations',
    'Ptah minicms example migration')

First parameter is package name, second parameter is asset style path and third parameter migration title.

• To create new revision you should use ptah-migrate script.

$ /bin/ptah-migrate settings.ini revision ptah_minicms -r 001 -m "Add column"
Generating /path-to-virtualenv/ptah_minicms/migrations/001.py...done

Generated script contains empty update() and downgrade() function. Add code that does migration from previous revision to this function.

• Now you can use ptah-migrate script to execute migration steps.

$ bin/ptah-migrate settings.ini upgrade ptah_minicms
2012-01-11 16:14:42,657 INFO  [ptah.alembic] ptah_minicms: running upgrade None -> 001

Check Data migration chapter for ptah-migrate script detailed description.

Migration data during start up

Use ptah_migrate() pyramid directive for migration data schema during startup.

import ptah
from pyramid.config import Configurator

def main(global_settings, **settings):

    config = Configurator(settings=settings)
    config.include('ptah')

    ...

    config.ptah_migrate()

    ...

    return config.make_wsgi_app()

Migration steps are executed after configration commited.

Notes

• Ptah stores package revision numbers in ptah_db_versions table. During data population process ptah checks if ptah_db_versions table contains version info, if it doesnt contain version information ptah just set latest revision without running migration steps. It assumes if there is no version information then database schema is latest.
• ptah-migrate script executes POPULATE_DB_SCHEMA populate step before running any upgrade steps.