Proper Realm usage patterns/best practices?

(Disclaimer: I work for Realm. I've left Realm now, but I'm still happy to help!) :)Thanks a lot! It's great to hear you're enjoying Realm!

Multiple Realm Instances -You don't need to worry about this at all! A Realm file object is created upon the first-time instantiation on each thread, and that same object is subsequently returned each time you try and instance it every time after that.

Retaining Realm Instances -Following on from the first point, no, you don't need to worry about hanging on to Realm reference inside other objects. As Realm tracks its Realm file objects internally and returns the same ones, you won't get penalised for not doing so. That being said, if having a permanent reference to a Realm object inside your object simplifies your code complexity, feel free to keep using it.

Accessing Realm Relationship Properties - Strictly speaking, data from Realm files aren't copied from disk (Like a normal ORM would do); more it uses memory mapping to directly reference the data from disk straight to your in-memory properties. So, no, you don't need to worry about Realm files getting too large in memory.

Auto-refreshAuto-refresh is only enabled by default for the Realm file object on the main thread. It has to be manually enabled for Realm file objects on other threads, or you can instead elect to manually refresh them with the refresh method call.

EDIT: I stand corrected! All Realm file objects on multiple threads have autorefresh on by default. When autorefresh is on, the only time you need to call refresh is if you need the changes made to a Realm file to be reflected in the other references before the current iteration of the run loop has completed.

Referencing an object's Realm referenceAbsolutely not, it's not bad practice at all! I actually prefer doing this in my own personal apps that use Realm to provide proper context since invariably it's easier, and provides stronger visual context between the object and its parent Realm file in the code. (Haha yep, if there was a threading problem here, you probably would have discovered it before even reaching the write point).

I hope that helped! Let me know if you need clarification on anything here!