I'm working on some scripts to export data from our current CMS (a custom in-house tool) to CiviCRM. This is a first import, and CiviCRM is a blank slate.
When importing activities it seems like the "Source Contact" column must be a civicrm ID.
I think this means I have to first import all the contacts, then pull a mapping from their CiviCRM ID to their external ID, and then import activities with the source contact column updated to match the CiviCRM ID.
Of course, this is entirely feasible, but if there's a simpler way to do this I'd love to know about it.