NSFetchRequest 检索每个学生在 CoreData 实体中每个科目的最高考试分数

Question

我有一个 CoreData 实体，在不同长度的比赛中有多个性能记录。我想在 each 比赛中获得 each 运动员的最佳表现，然后将结果放入 CoreData Table 视图中。

这是我为完成此任务而想出的技巧。但是，这会影响我将结果放入 Table 视图中，其中比赛距离为 headers 部分：

- (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];

以下块中的代码是我为每个运动员提取最佳表现的地方。

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];

NSArray bestMarks 有 27 个 NSManagedObjects，而提取请求返回 35 个。

下面的代码是我过去和仍然喜欢填充我的 CoreData TableView 的方式。

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];
}
}

有没有办法用 NSFetchRequest 谓词来做到这一点？

或者我可以通过将 Managed Objects 放入 NSDictionaries 的 NSArray 中来创建部分，其中每个 NSDictionary 是不同的比赛距离吗？

感谢您的帮助。如果我完全偏离了正确的道路并且有更有效的方法来实现这一点，我也很高兴知道！

Answer 1

好的，这就是我的想法。希望这可以帮助其他人：我根据 "class"（在我的例子中是种族）将托管对象解析为 NSMutableArrays。然后我将每个 NSM 数组放入一个 NSMutableDictionary 中，其中索引作为键。该字典及其中的数组随后成为确定节数和节中行数的基础。

- (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];

}

过滤数据后不得不做一个度假村。可能有更有效的方法来执行此操作，但这种蛮力方法有效，因为我在这种方法中从 Core Data 中提取的记录相对较少。

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