Thanks for this tip! 
I’m starting to think about that this would make a good new module - although a rather small one for just a simple feature. Controller::join_links() is already a step towards a more cleaner solution than what I have been using so far. Now I just need to plan how to implement the “chaining” feature that I mentioned above (= I’ll think about the easiest way to define a kind of notation for "get URL for this Book via its Library"). Maybe I should also take a look at how GridField scaffolds links to editable records.