Question

当我尝试在iPhone Core-Data应用程序中的列上获取@sum时，我遇到了异常。

我的两个模型正在关注 -

任务模型：

@interface Task :  NSManagedObject
{

}

@property (nonatomic, retain) NSString * taskName;
@property (nonatomic, retain) NSSet* completion;

@end

@interface Task (CoreDataGeneratedAccessors)
- (void)addCompletionObject:(NSManagedObject *)value;
- (void)removeCompletionObject:(NSManagedObject *)value;
- (void)addCompletion:(NSSet *)value;
- (void)removeCompletion:(NSSet *)value;

@end

完成模型：

@interface Completion :  NSManagedObject
{
}

@property (nonatomic, retain) NSNumber * percentage;
@property (nonatomic, retain) NSDate * time;
@property (nonatomic, retain) Task * task;

@end

这是获取：

NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"Task" inManagedObjectContext:context];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"taskName" ascending:YES];
request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
NSError *error;
NSArray *results = [context executeFetchRequest:request error:&error];
NSArray *parents = [results valueForKeyPath:@"taskName"];
NSArray *children = [results valueForKeyPath:@"completion.@sum.percentage"];
NSLog(@"%@ %@", parents, children);
[request release];
[sortDescriptor release];

从底部第四行抛出异常。抛出的异常是：

*** -[NSCFSet decimalValue]: unrecognized selector sent to instance 0x3b25a30
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSCFSet decimalValue]: unrecognized selector sent to instance 0x3b25a30'

我非常感谢任何帮助。感谢。

编辑：我在雪豹10.6.3和SDK 3.1.3。

Answer 1

如果要计算每个任务的总完成百分比总和，可以在任务类中为“completionSum”实现一个getter

// interface (Task.h)
@property (nonatomic, readonly) NSNumber* completionSum;    

// implementation (Task.m)
-(NSNumber*) completionSum
{
    return [self valueForKeyPath:@"completion.@sum.percentage"];
}

使用@sum计算速度很慢，此解决方案不符合KVO标准。如果您需要这些，您应该考虑使用KVO实施解决方案。

我已经发布了指向此问题的开源解决方案的链接（http://qr.cx/FVi）

核心数据@sum聚合

1 个答案: