Calculating the max value for a core data attribute - NSCFNumber error

Question

I need to find out the maximum value of an attribute of a core data entity.

I\'m still firmly in the Cocoa learning curve, and this is a simple test app that I\'m us

Answer 1

I had to solve a similar problem and approached it slightly differently by:

• querying the entity
• ordering by the attribute you want
• limit the fetch results to 1

The code for this is below. I am querying an entity called 'entityName' and retrieving the max value for the attribute 'sequenceId'.

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *res = [NSEntityDescription entityForName:@"entityName" inManagedObjectContext:managedObjectContext];
[request setEntity:res];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"sequenceId" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[request setSortDescriptors:sortDescriptors];
[sortDescriptors release];
[sortDescriptor release];

[request setFetchLimit:1];

NSError *error = nil;
NSArray *results = [managedObjectContext executeFetchRequest:request error:&error];
[request release];
if (results == nil) {
    NSLog(@"error fetching the results: %@",error);
}

NSInteger maximumValue = 0;
if (results.count == 1) {
    Result *result = (Result*)[results objectAtIndex:0];
    maximumValue =  [result.sequenceId integerValue];
}