This article is part of a series about my deployment workshop on the T3DD13. Make sure to read the other posts, too.
Idea of „migrations“ for more then database schema updates
This basic concept of „migrations“ for TYPO3 CMS goes back to a talk on the T3DD in 2009 I held together with Christopher. Back then we implemented a Proof of Concept for a customer project and presented that on the devdays.
In that project we had multiple installations (like the live system, a staging sytem, and several developer systems) and needed to apply the same changes to all those independent systems. Those „changes“ were things like templavoila TO/DS and mappings, setting up pages with configured plugins, application related configurations in the database and so on. Basically everything one need to do in the backend.
We started to maintain a wiki page and collected all changes (as a step-by-step guide) which need to be done on the next release. Whenever someone updates the codebase on one of the systems, he needs to check the wiki what needs to be done in the backend. This approach was very time-consuming and error-prone. So we wanted to be able to script all these changes and deliver them with the code base in the project SVN (we didn’t used Git back then) and be able to track which changes are already done on one system and which are missing.
From Ruby or Doctrine you might know the concept of migrations. It’s basically made for database schema updates, like creating a new table, adding columns or updating column definitions. A migration provides update from one stage of the database to a new one. A migration can be „applied“ („up“ or „execute“) or „removed“ („down“ or „rollback“). Each installation „knows“, which migrations are already applied and which are not. With a simple command you can apply all missing migrations (in the correct order) to make sure your database is up to date.
In TYPO3 we have a solution for database schema updates already: The „database compare tool“ compares the current database table definitions with those described in the ext_tables.sql files in the extensions. But we can make use of this basic concept to solve the issues described above.
A migration is basically a PHP class with a certain naming convention and in a defined folder. As it is just a file, it can be versionized and distributed to all instances using the VCS (e.g. Git or SVN). Each migration class has a „up“, a „down“ method and a unique identifier (a UUID, a timestamp or something else).
Each instance knows which migrations are available (by scanning the defined folders for migration class files) and which of them are already applied. In a backend module and by using a CLI command the user can list and run the missing migrations. This will call the „up“ method for each migration and memorize all successfully applied migrations.
As the migrations as just PHP classes, you can do everything you need within the „up“ (and the „down“) methods. For example it can use the service classes provided by EXT:coreapi to create/update records.
I see a lot of use cases for such a tool and I’m sure it will help a lot to solve the issue of not-versionized configuration and application related data, which are in the database of TYPO3, but not in files currently.
All described above is just ideas and concept. There is no implementation yet. I’m willing to work on a proof of concept and a first implementation. If you like the idea, if you need something like that or have any suggestions, please get in touch with me!