Is there some existing migration code for converting ATTopic instances (we export them using collective.jsonify) to Collections in Plone 5? Is there migration code for Transmogrifier or should I look at the migration code in Plone 5?
The builtin migration migrates Topics as well as AT-based Collections to DX-collections. I just migrated a large DB that had with 300 Topics (and more than 20.000 Files) from 4.3 on AT to 5.2 on DX. See https://github.com/plone/plone.app.contenttypes#migrating-topics for infos regarding subtopics.
See https://github.com/plone/plone.app.contenttypes/blob/master/plone/app/contenttypes/migration/topics.py for the code used to migrate Topics.
We used that code Philip mentions to migrate ATTopics to Collections via Transmogrifier. Maybe it is time to throw all those things we build together?
Releasing the migration pipeline that I am currently working on for the University of Gent should not be a problem
The rough outline is here:
It includes already the migration from PFG -> Easyform and only needs the Topic -> Collection to migration.