聚合函数上的 iOS FetchRequest：如何包含挂起的更改？

我终于至少缩小了这个问题的范围。我正在计算支出的一些聚合函数（如本例中的总和）。如果我更改一些支出，此聚合提取不会立即刷新，而是在一段时间后刷新（可能是在更改保存到数据库之后）。我在文档中找到了这部分：

- (void)setIncludesPendingChanges:(BOOL)yesNo

根据文档

值为YES不支持与结果类型结合使用NSDictionaryResultType，包括汇总结果的计算 （例如最大值和最小值）。对于字典，从返回的数组 fetch 反映了持久存储中的当前状态，而不是 考虑任何未决的更改、插入或删除 语境。如果您需要考虑某些待定更改 像 max 和 min 这样的简单聚合，您可以使用普通的聚合 获取请求，根据您想要的属性排序，获取限制为 1.

好的，我怎样才能仍然包含待处理的更改？我正在使用一个NSFetchedResultsController显示我的数据。这是我的聚合函数：

- (NSNumber *)getExpendituresAmountForCostPeriod:(CostPeriod)costPeriod
{
    NSLog(@"getExpenditures_Start");
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Expenditures"];
    [fetchRequest setResultType:NSDictionaryResultType];

    NSDate *startDate = [NSDate startDateForCostPeriod:[self getBiggestCostPeriod]];
    fetchRequest.predicate = [NSPredicate predicateWithFormat:@"forSpendingCategory = %@ AND date >= %@", self, startDate];        

    //Define what we want
    NSExpression *keyPathExpression = [NSExpression expressionForKeyPath: @"amount"];
    NSExpression *sumExpression = [NSExpression expressionForFunction: @"sum:"
                                                            arguments: [NSArray arrayWithObject:keyPathExpression]];

    //Defining the result type (name etc.)
    NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
    [expressionDescription setName: @"totalExpenditures"];
    [expressionDescription setExpression: sumExpression];
    [expressionDescription setExpressionResultType: NSDoubleAttributeType];

    // Set the request's properties to fetch just the property represented by the expressions.
    [fetchRequest setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]];
    NSLog(@"%@", self.managedObjectContext);

    // Execute the fetch.
    NSError *error = nil;
    NSArray *objects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    if (objects == nil) {
        return [NSNumber numberWithDouble:0];
    } else {
        if ([objects count] > 0) {
            return [[objects objectAtIndex:0] valueForKey:@"totalExpenditures"];
        } else {
            return [NSNumber numberWithDouble:0];
        }
    }
}

EDIT: *是一个循环NSSet可能并且足够快吗？*

- (NSNumber *)getExpendituresAmountForCostPeriod:(CostPeriod)costPeriod
{
    NSDate *startDate = [NSDate startDateForCostPeriod:[self getBiggestCostPeriod]];
    double total = 0;

    for(Expenditures *expenditure in self.hasExpenditures){
        if(expenditure.date >= startDate){
            total = total + [expenditure.amount doubleValue];
        }
    }

    return [NSNumber numberWithDouble:total];
}

最后编辑并给出答案感谢大家，我终于在循环中找到了问题。这工作得非常快而且很好：

- (NSNumber *)getExpendituresAmountForCostPeriod:(CostPeriod)costPeriod
{
    NSDate *startDate = [NSDate startDateForCostPeriod:[self getBiggestCostPeriod]];
    double total = 0;

    for(Expenditures *expenditure in self.hasExpenditures){
        if([expenditure.date compare: startDate] == NSOrderedDescending){
            total = total + [expenditure.amount doubleValue];
        }
    }

    return [NSNumber numberWithDouble:total];
}

从controllerDidChangeContent 调用。

今天就够了..:-)

您的解决方案没问题，但您仍然可以通过首先缩短集合然后利用 KVC 避免循环来加快速度并生成更短的代码：

NSSet *shortSet = [self.hasExpenditures filteredSetUsingPredicate:
  [NSPredicate predicateWithFormat:@"date > %@", startDate]];
NSNumber *total = [shortSet valueForKeyPath:@"@sum.amount"];