NSDecimalNumber总和

Question

在我的ios项目中，我使用了两个实体（ CoreData ）：具有多对多关系的人和礼物

我知道如何计算一个人的礼物总数：

NSDecimalNumber *orderSum=[person.gifts valueForKeyPath:@"@sum.priceOfGift"];

但我如何计算所有人的总和？

 -(NSFetchedResultsController *) fetchedResultsController {
if (_fetchedResultsController != nil) {
    return _fetchedResultsController;
}
//NSError *error = nil;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Person"
                                          inManagedObjectContext:[self managedObjectContext]];
[fetchRequest setEntity:entity];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"nameOfPerson"
                                                               ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];


_fetchedResultsController = [[NSFetchedResultsController alloc]initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"nameOfGroup" cacheName:nil];

_fetchedResultsController.delegate = self;

return _fetchedResultsController;

}

Answer 1

所有人的总和＆＃34;将是取所有人并计算他们

int sum = fetchedObjects.count;

但也许你的意思是所有人的所有礼物价格的总和＆＃34;。如果您考虑一下，它与所有礼品的价格总和相同。因此，您只需获取礼物并计算

即可

NSNumber *sum = [self.fetchedResultsController.fetchedObjects 
      valueForKeyPath:@"@sum.priceOfGift"];

Answer 2

您可以尝试获取所有人员，然后使用总和

    NSError *error = nil;
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    request.entity = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:managedObjectContext];
    request.predicate = nil;
    request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"index" ascending:YES]];//some parameter
    NSArray *persons =  [managedObjectContext executeFetchRequest:request error:&error];
 NSDecimalNumber *orderSum;
 for (Person *person in persons)
  orderSum = [NSDecimalNumber decimalNumberWithDecimal:orderSum.decimalValue
+[person valueForKeyPath:@"gifts.@sum.priceOfGift"].decimalValue]

虽然，现在使用NSDecimalNumber看起来有点不舒服。