CODEWITHSUNDEEP
iphonecocoacore-data
jvliwanag
jvliwanag

Reputation: 1598

Core Data Problem - select group by/having max

Say I have two Entities:

Entities

Each Message belongs to a single MessageThread. How do I get all the message threads and the corresponding last message on that thread? Normally, in SQL, I'd do it as:

select __ from message group by thread having timeStamp=max(timeStamp)

For one, I don't think Core Data allows the @max in its predicates. Any ideas?

Upvotes: 3

Views: 1052

Answers (2)

Gilad Novik
Gilad Novik

Reputation: 4604

This might be a bit old, but I had a similar problem recently. Here is my solution to the problem:

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Message"];
request.predicate = [NSPredicate predicateWithFormat:@"timeStamp = [email protected]"];
request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"timeStamp" ascending:NO]];

I hope it helps...

Upvotes: 3

Olaf
Olaf

Reputation: 3042

I could never get @max to work and I still look for a better implementation.

What I do as a porkaround is to set the sort descriptor to order by date and then use the objectAtIndex:0 from the fetchedResults.

Upvotes: 0

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