Presentation

In Wikitty, migration is done each time you load an object. If an object is present in the database in an old version, when it is loaded from the database, it is automatically migrated to the new version. This way, you avoid costly migration at initialisation.

The only thing to bear in mind is that data which was not migrated is still indexed in the old version and might not be returned by requests. If you need the data to be indexed on the new version, you still can migrate all your objects at initialisation by loading all the objects and store them.

How migrate data properly in Wikitty

After your application launch and before any request, you should store all the extensions needed by your application, in their last version

store(myExtension);

Then you need to add to the registry all the specific migrations for extensions:

WikittyExtensionMigration.migrationRegistry.put("myExtension", myMigrationClass);

You can now use your data properly, they will be migrated at loading time.

If you want to migrate objects before using them (for requests purpose for example), for each version, search all you objects, restore and then store them:

search(Client)
restore(Client)
store(Client)

Take care to the cost of the indexation compared to the data volume.

Specific migrations

Wikitty makes an automatic migration in cas of deleted fields, added fields or renamed fields (need to add a renameFrom tag on the field).

For other kind of migration, you might want to create your own migration class that implements WikittyExtensionMigration. This class only needs to make the migration from a version to the next version, for example version 1 to version 2. In cas of a migration needed from version 1 to version 4, Wikitty will automatically call the classes to migrate form version 1 to 2, then from version 2 to 3 and so on.