Question

That is, I have an entity A with a to-many relationship with entity B. B instances have, among other attributes, a creationDate. And I also already have a managed object for A in memory.

So I know I can access all B instances through A’s accessor. But I’d like to do something along the lines of:

“for all Bs in A.relationshipName, return the managed object for the B with the most recent B.creationData”

How could I go about it?

Answer 1

Alternately, since you already have a managed object A in memory, you could do an in-memory filtered sort of the A->>B relationship.

A *inMemoryA = ...

id byDate = [NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:YES];
id sorters = [NSArray arrayWithObjects:byDate, nil];
NSArray *sortedBs = [inMemoryA allBs] sortedArrayUsingDescriptors:sorters];

B *mostRecentB = [sortedBs lastObject];