NSFetchRequest to retrieve Every Student's Maximum Test Score for Every Subject in CoreData Entity

Question

I have a CoreData Entity with multiple performance records in races of differing length. I want to pull the best performance for each athlete in each race and then put the results in an CoreData Table View.

Here is the hack that I have come up with to accomplish this. However, this interferes with my ability to put the results into a TableView where the race distances are section headers:

- (void)setupFetchedResultsController // attaches an NSFetchRequest to this UITableViewController
{
MarksFromMeets* results = nil;

NSMutableArray * bestMarks = [[NSMutableArray alloc] init];


NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"MarksFromMeets"];

//    NSLog(@"self.athlete.athleteID = %@",self.athlete.athleteID);

request.predicate = [NSPredicate predicateWithFormat:@"(ANY whoRan.athleteID in %@) AND (eventPR > 0)",
                     self.athleteIDsForPredicate];
/* Call the records for selected athletes (PLURAL) */


request.sortDescriptors = [NSArray arrayWithObjects:
                           [NSSortDescriptor sortDescriptorWithKey:@"whoRan.athleteID" ascending:NO],
                           [NSSortDescriptor sortDescriptorWithKey:@"event" ascending:YES],
                           [NSSortDescriptor sortDescriptorWithKey:@"sortMark" ascending:YES],
                           nil];

The code in the following block is where I pull out best performance for each athlete.

NSArray * allMarks = [self.headToHeadManagedObjectContext executeFetchRequest:request error:nil];

MarksFromMeets* tempMark;

for (MarksFromMeets* athletePRs in allMarks) {

    if (tempMark == nil) {
        tempMark = athletePRs;
    } else {
        if ([athletePRs.whoRan.athleteID isEqualToString:tempMark.whoRan.athleteID]) {
            if ([athletePRs.event isEqualToString:tempMark.event]) {
                if (athletePRs.sortMark < tempMark.sortMark) {
                    tempMark = athletePRs;
                }
            } else {
                [bestMarks addObject:tempMark];
                tempMark = athletePRs;
            }
        } else {
            [bestMarks addObject:tempMark];
            tempMark = athletePRs;
        }
    }
}
if (debug == 1) NSLog(@"bestMarks count: %lu \nallMarks count: %lu", (unsigned long)[bestMarks count], [allMarks count]);

[self setResultsArray:bestMarks];

The NSArray bestMarks has 27 NSManagedObjects, whereas the fetch request returned 35.

The code below is how I use to, and would still prefer to, populate my CoreData TableView.

self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                    managedObjectContext:self.headToHeadManagedObjectContext
                                                                      sectionNameKeyPath:@"event"
                                                                            cacheName:nil];

NSError* error = nil;

results = [[self.headToHeadManagedObjectContext executeFetchRequest: request error:&error]objectAtIndex:0];

NSError* requestError = nil;
NSUInteger myCount = [self.headToHeadManagedObjectContext countForFetchRequest:request error:&requestError];
NSLog(@"In %@ and count of results = %lu", NSStringFromClass([self class]),(unsigned long)myCount);
if (!myCount || myCount == 0) {
    NSMutableString* titleText = [NSMutableString stringWithFormat:@"No Records Found"];
    NSMutableString* messageText = [NSMutableString stringWithFormat:@"There were no records found for the %lu athletes selected. Contact ITrackPerfomance using this list of Athlete ID's: %@",  (unsigned long)[self.athleteIDsForPredicate count], self.athleteIDsForPredicate];

    NSString* cancelText = @"Okay";

    [self displayAlertBoxWithTitle:(NSString*)titleText message:(NSString*) messageText cancelButton:(NSString*) cancelText];
}
}

Is there a way to do this with a NSFetchRequest predicate?

Or can I create sections by putting the Managed Objects into an NSArray of NSDictionaries where each NSDictionary is a different race distance?

Thanks for your help. If I am totally off the right path and there is a more efficient way to accomplish this, I would be glad to know that too!

Answer 1

Okay, here is what I came up with. Hope this helps others out: I parsed the Managed Objects into NSMutableArrays based upon the "class" (race in my case). Then I used put each NSM Array into a NSMutableDictionary where an index acted as the key. This dictionary and the arrays within it then became the basis for determining the number of sections and the the number of rows in sections.

- (void)setupFetchedResultsController // attaches an NSFetchRequest to this UITableViewController
{
MarksFromMeets* results = nil;

NSMutableArray * bestMarks = [[NSMutableArray alloc] init];
NSMutableDictionary * dictionaryOfMarksByRace = [[NSMutableDictionary alloc] init];

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"MarksFromMeets"];

//    NSLog(@"self.athlete.athleteID = %@",self.athlete.athleteID);

request.predicate = [NSPredicate predicateWithFormat:@"(ANY whoRan.athleteID in %@) AND (eventPR > 0)",
                     self.athleteIDsForPredicate];
/* Call the records for selected athletes (PLURAL) */


request.sortDescriptors = [NSArray arrayWithObjects:
                           [NSSortDescriptor sortDescriptorWithKey:@"event" ascending:YES],
                           [NSSortDescriptor sortDescriptorWithKey:@"whoRan.athleteID" ascending:NO],
                           [NSSortDescriptor sortDescriptorWithKey:@"sortMark" ascending:YES],
                           nil];


NSArray * allMarks = [self.headToHeadManagedObjectContext executeFetchRequest:request error:nil];

MarksFromMeets* previousMark;

int i = 0;
int j = 0;
for (MarksFromMeets* athletePRs in allMarks) {
    NSArray* sortedMarks;
    if (previousMark == nil) {
        previousMark = athletePRs;
    } else {
        if ([athletePRs.event isEqualToString:previousMark.event]) {
            if ([athletePRs.whoRan.athleteID isEqualToString:previousMark.whoRan.athleteID]) {
                NSLog(@"athletePRs.%@ = previousMark.%@",athletePRs.sortMark,previousMark.sortMark);


                if ([athletePRs.sortMark intValue] < [previousMark.sortMark intValue]) {
                    previousMark = athletePRs;
                    NSLog(@"Should NEVER happen");
                }
            } else {
                [bestMarks addObject:previousMark];
                NSLog(@"Adding %@, %@, %@ to bestMarks for i = %d",previousMark.event, previousMark.markInEvent, previousMark.whoRan.athleteFullName,i);
                previousMark = athletePRs;
                NSLog(@"tempMark record now %@",previousMark.whoRan.athleteFullName);
                if (j == [allMarks count]-1) {
                    [bestMarks addObject:previousMark]; //Now tempMark is last MarksForMeet object
                    sortedMarks = [self sortNSMutableArray:bestMarks];
                    [dictionaryOfMarksByRace setObject:sortedMarks forKey:[NSNumber numberWithInt:i]];
                    bestMarks = [[NSMutableArray alloc] init];

                }
            }
        } else {
            [bestMarks addObject:previousMark];
            previousMark = athletePRs;
            sortedMarks = [self sortNSMutableArray:bestMarks];
            [dictionaryOfMarksByRace setObject:sortedMarks forKey:[NSNumber numberWithInt:i]];
            NSLog(@"Adding %@ to bestMarks for i = %d",previousMark.event,i);
            bestMarks = [[NSMutableArray alloc] init];
            // reallocate bestMarks to ensure values in NSMutableDictionary are unique
            i++;
            if (j == [allMarks count]-1) {
                [bestMarks addObject:previousMark];
                sortedMarks = [self sortNSMutableArray:bestMarks];
                [dictionaryOfMarksByRace setObject:sortedMarks forKey:[NSNumber numberWithInt:i]];
                bestMarks = [[NSMutableArray alloc] init];
                // reallocate bestMarks to ensure values in NSMutableDictionary are unique
            }
        }
    }
    j++;
}


[self setResultsDictionary:dictionaryOfMarksByRace];

}

Had to do a resort after filtering the data. There may be a more efficient way of doing this, but this brute force method works since I am pulling relatively few records from Core Data in this method.