Question

I store time periods in Core Data. Each time period has an DateTime attribute called EndDate. I am trying to get the maximum end date, which is before (<) the date specified.

This is how I have coded this using a subquery and ValueForKeyPath:

NSString *keyPath = [NSString stringWithFormat:@"SUBQUERY(SELF, $x, $x.EndDate < %@)[e-mail]", date];
IBFinPeriod *periodBeforeCurrentDate = [self.finperiod valueForKeyPath:keyPath];

However, when running this code, I get the runtime error: the entity IBFinPeriod is not key value coding-compliant for the key "SUBQUERY(SELF, $x, $x".'

What is wrong with my code?
Do I need to specify the subquery differently?

Thank you for your help!!

Answer 1

You could use a fetch request with fetchLimit set to 1 and a descending sort descriptor.

If you insist on the valueForKeyPath: I would first filter the results with filteredArrayUsingPredicate: (with a straight forward predicate selecting the records with dates prior to your date) and then simply using @"@max.EndDate" as the key path.

If you need the entire object rather than just the date, just sort your set:

NSSet *periodsBeforeCurrentDate = [self.finperiod 
    filteredSetUsingPredicate:[NSPredicate predicateWithFormat:
       @"EndDate < %@", date]];
if (periodsBeforeCurrentDate.count) {
    *sort = [NSSortDescriptor sortDescriptorWithKey:@"EndDate" ascending:NO];
   NSArray *sortDescriptors = [NSArray arrayWithObject:sort];
   IBFinPeriod *lastPeriodBeforeCurrentDate =[[periodsBeforeCurrentDate 
       sortedArrayUsingDescriptors:sortDescriptors] objectAtIndex:0];
}

In my opinion it would be easier to just fetch.