How to efficiently get all instances from deeper level in Cocoa model?
- by Johan Kool
In my Cocoa Mac app I have an instance A which contains an unordered set of instances B which in turn has an ordered set of instances C. An instance of C can only be in one instance B and B only in one A.
I would like to have an unordered set of all instances C available on instance A. I could enumerate over all instances B each time, but that seems expensive for something I need to do often. However, I am a bit worried that keeping track of instances C in A could become cumbersome and be the cause of inconsistencies, for example if an instance C gets removed from B but not from A.
Solution 1
Use a NSMutableSet in A and add or remove C instances whenever I do the same operation in B.
Solution 2
Use a weak referenced NSHashTable in A. When deleting a C from B, it should disappear for A as well.
Solution 3
Use key value observing in A to keep track of changes in B, and update a NSMutableSet in A accordingly.
Solution 4
Simply iterate over all instances B to create the set whenever I need it.
Which way is best? Are there any other approaches that I missed?
NB I don't and won't use CoreData for this app.
