Take a domain class: class ArtistMonitor { static belongsTo = UserProfile UserProfile userProfile Artist artist } If you do new ArtistMonitor().save() you get no errors, even though there are missing references. All columns default to nullable: false and optional: false apparently, so why is this happening? Also, and with more complexity, you get no errors when saving the class that references this i.e: def u = new UserProfile( ...) u.addArtistMonitor(new ArtistMonitor()) u.save() No errors at all occur. If you save the monitor first explicitly, still no errors exist on the artistMonitor instance. Related to GRAILS-890 possibly.