When topic is closed, we mark assignments as "inactive". Then when it is reopen and setting reassign_on_open is enabled, we bring back previous assignments.
We were already using custom fields for archive message and move to inbox. I changed custom fields solution to use active flag on Assignment model
When post is already assigned to user/group then don't allow assigning a topic to that user/group.
Similarly, right now when topic is already assigned we are not allowing to assign a post that that user.
Build a new workflow that adds a dropdown in place of the old assign button with the ability to
Re-assign a new user / group to an assigned topic
Re-assign yourself to an assigned topic
Unassign a user / group from an assigned topic
Change `topic_id` to polymorphic approach (In the next step we will allow assigning to individual post)
`topic_id` column is still used for efficient display of assigned users on topic list (to avoid scanning posts)
Krzysztof Kotlarek
janzenisaac