I've got from other colleagues of mine a layer of buildings (polygons) and a few tables with data about the buildings (without geometry).
This layer is related to the tables with relations in arcmap thanks to a common fields (ID_BUILDING, string(12)). 1-M relations can exist (1 building gets 5 floors).
I would like to publish this on ArcGIS Online. When I create new databases I use to create a GlobalID on my layer and a GUID field in my related table and then create a class of relationship. And it works well.
How can I use/transfert/convert the field ID_BUILDING to create a class of relationship that will keep the relations between my tables ?
I think you can just create a series of relationship classes between your polygons and tables and then publish the whole thing. You might want to consider migrating to ArcGIS Pro, I think it works better than ArcMap when dealing with AGOL.