IOS/ objective-c /核心数据 : Sum all the values for an attribute from query

Question

我想在从核心数据中获取数据后将某个属性的所有值相加。是否有一些快捷方式，例如 sum 可以快速返回它。

这是我的标准获取代码。寻找可以将 orderprice 的值相加以获得所有订单总和的东西

- (id) getSalesTotal{
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Orders"];
    fetchRequest.resultType = NSDictionaryResultType;

    NSError *error      = nil;
    self.managedObjectContext = [IDModel sharedInstance].managedObjectContext;

    NSArray *results    = [self.managedObjectContext executeFetchRequest:fetchRequest
                                                                   error:&error];
    NSLog(@"error is %@",error);
    // NSLog(@"context%@",results);
    NSLog(@"beforevalueforkey%@",results);
    NSMutableArray * ordertotal = [[results valueForKey:@"orderprice"] mutableCopy];
    return ordertotal;//Is there something like sum(ordertotal)?????
}

Answer 1

您可以使用键值编码:

NSNumber *orderTotal = [arrayWhoseSumIsToBeCalculated valueForKeyPath:@"@sum.self"];