You could consider the following approaches:
- links between tables
-
row.get_id()(but please do not rely on the format of this string as it may change) - creating your own UUID
I maintain a portal where users are associated with multiple media resources as well as multiple roles. This is all handled by using links between tables (the first bullet point above). With this approach, it makes it very easy to set and get the connections that are associated with any user (without having to maintain explicit IDs).
There are many approaches that could work and certainly I do rely on get_id() as well as UUIDs in other applications. This is just what comes to mind based on your description.