The main data problem - select the group by / s max.

Question

Let's say I have two entities:

Each message belongs to one MessageThread. How to get all message flows and the corresponding last message in this thread? Typically, in SQL, I would do it like:

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

First, I don’t think Core Data allows @max in its predicates. Any ideas?

Answer 1

It may be a little old, but lately I have had a similar problem. Here is my solution to the problem:

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

Hope this helps ...

Answer 2

I could never work @max , and I'm still looking for a better implementation.

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