Question

I have a web service call that returns XML which I convert into domain objects, I then want to insert these domain objects into my Core Data store.

However, I really want to make sure that I dont insert duplicates (the objects have a date stamp which makes them unique which I would hope to use for the uniqueness check). I really dont want to loop over each object, do a fetch, then insert if nothing is found as that would be really poor on performance…

I am wondering if there is an easier way of doing it? Perhaps a “group by” on my objects in memory???? Is that possible?

Answer 1

Your question already has the answer. You need to loop over them, look for them, if they exist update; otherwise insert. There is no other way.

Since you are uniquing off of a single value you can fetch all of the relevant objects at once by setting the predicate:

[myFetchRequest setPredicate:[NSPredicate predicateWithFormat:@"timestamp in %@", myArrayOfIncomingTimestamps]];

This will give you all of the objects that already exist in a faulted state. You can then run an in memory predicate against that array to retrieve the existing objects to update them.

Also, a word of advice. A timestamp is a terribly uniqueID. I would highly recommend that you reconsider that.