Core Data Fetching Objects That Are in Relationship to another object
cocoa, core-data, iphone, objective-c
Solution
You must specify a reverse relationship in Class B in order to do what you are asking.
However, I'm not sure why you are objecting (no pun intended) to grabbing the set of B objects already in object A. Even though the objects themselves are lazy loaded, since you already have A in memory, I have a hunch (although an expert would need to verify) that it would be more efficient to simply grab the set from A than to specify a new NSPredicate, and create a completely new Fetch.
Of course, by "more efficient" we're talking milliseconds, even on a device as slow as the iPhone. I'd grab the set from object A because the syntax is cleaner. The fact that it may also be faster is a bonus.
Problem
I want to fetch objects B which has a to-many relationship with object A (ie. A -->> B). I already have A in memory. I know I could get a NSSet of the B objects from A, but would it be better to make a fetch request of the B objects (especially if I want to sort sections by date in a UITableView)? How would I make such a request that only gets the B objects belonging to a single object A?