Allow admins to merge user accounts

[RichiH]

Problem and impact

Sometimes, users register more than one account. It is currently not possible for admins to merge those users into one account.

Proposed solution / feature

Admins should be able to merge user accounts.

Context or examples

No response

[johanvdw]

So looking at the reverse relationships of users, the actual merge seems relatively easy: choosing one base User and moving those relationships or removing them (eg I would not move the token). https://docs.pretalx.org/developer/interfaces/models.html#users-and-profiles

The bigger question seems to be how you would find two users that can be merged as there is no real user interface for listing users across conferences. Perhaps that is needed as well.

[rixx]

This feature would be restricted to administrators. I do think having a list of registered users for superusers/administrators would be good.

[johanvdw]

FYI, we had quite a number of duplicate users, and I ended up creating a management script
https://github.com/FOSDEM/pretalx-integration/blob/master/devroom-settings/devroom_settings/management/commands/merge_users.py
not super nice, but it works.

[rixx]

Thanks! That does look like a good start – fwiw, you'll probably want to also migrate ActivityLog objects (although I know you handle your audit logging separately).