The Odoo Migration Manager

The core mechanism that OpenUpgrade relies on is the migration manager that is already built into Odoo itself. It is this mechanism that was used by Odoo to run migrations back in the days before TinyERP 4.2 when migration scripts where still included in the code. The same mechanism is probably still used by Odoo internally to run the proprietary migration, and occasionally it is used in the code to fix glitches during the Odoo release lifecycle. For an example, see https://github.com/odoo/odoo/commit/8b02879ff5.

Please have a look at the docstring of the Odoo migration manager: https://github.com/odoo/odoo/blob/7c95c14c06d77e5ebbd7aafd9c0c345b47d27d30/odoo/modules/migration.py#L23. You will see that migration scripts are organized in the migrations subdirectory in the module itself, in subdirectories per module version. The scripts will be executed when the module is upgraded, if the installed version of the module is lower than the name of the versioned directories.

There are three migration stages at which you can have migration scripts executed: before the module is loaded (pre stage), after the module is loaded into the database (post stage) and when all the modules are loaded (end stage). The end stage was introduced into Odoo 9.0. In earlier versions of OpenUpgrade, a file odoo/openupgrade/deferred_<VERSION>.py was maintained to collect migration steps to be run after a full upgrade.

Note that you can use this mechanism for your own custom module’s lifecycle outside of the OpenUpgrade context. For that reason, the OpenUpgrade helper methods were collected into the python openupgradelib that you can make available in any Odoo instance using the pip tool.