I have created a number of attribute rules that populate a given field from underlying feature layers (thanks to Xander Bakker). Now I would like to update a feature layer attribute from a related table. In Frequently Asked Questions | ArcGIS for Developers the question How do I access data from related tables sends you to the Featureset page. But I don't see anything there regarding a related table.
In a nutshell, I have a feature layer of City polygons that I would like to relate to a table of corresponding three letter city codes. When I add a new feature (centerline, address point etc) I can update the City name easily, but how would I update that City code from a related table? I'd like to avoid adding yet another field to the City features. Both the feature layer and related table will reside in the same $datastore, an enterprise geodatabase.