0

我正在使用名为CrumbPoint存储纬度和经度的核心数据实体，它指向（与）另一个名为HRRecord. CrumbPoint 是这样创建的：

CrumbPoint *crumbPoint = [NSEntityDescription insertNewObjectForEntityForName:@"CrumbPoint"
                                                       inManagedObjectContext:context];
crumbPoint.lat = [NSNumber numberWithFloat:lat];
crumbPoint.lon = [NSNumber numberWithFloat:lon];
crumbPoint.velocity = [NSNumber numberWithFloat:velocity];
crumbPoint.date = [NSDate date];

// Since this use search query, always refresh from DB
// The following fetch using NSFetchRequest when the record is available.
HrRecord * hr = [HRRecord hrRecordWithTitle:title inManagedObjectContext:context];
crumbPoint.inRecord = hr;

HrRecord 有一个名为的字段distance，只要设备有位置更新，我就需要更新该字段。（我正在跟踪用户慢跑）。对于每个位置更新，CrumbPoint都会创建一个新的，它指向HrRecord相同的慢跑会话。需要计算先前位置和新位置之间的新距离并且HrRecord需要更新距离。

但是我的问题是每次我得到 HrRecord （也许这是一个糟糕的设计，但我每次都NSFetchRequest用来查询新的位置更新。）HrRecord

现在当我尝试更新时：

HrRecord * hr = crumbPoint.inRecord;
float oldDistance = [hr.distance doubleValue];
// code to calculate distance here, then, update
hr.distance = [NSNumber numberWithDouble: newDistanceUpdate];

hr.distance更新前总是 0，即使每次更新后我都可以打印出新值。我尝试发送save到托管对象上下文，但它似乎也不起作用。这是为什么？

编辑：这是插入的代码。也许该错误与保存无关，在保存上下文后，我尝试拉出记录[HrRecord HrRecordWithTitle:title inManagedObjectContext:context]并为该轮更新距离。但是下次位置更新时，由于某种原因，它再次为 0。我必须检查更多代码。：/

+(HrRecord *)HrRecordWithTitle: (NSString *)title
                      inManagedObjectContext:(NSManagedObjectContext *)context
{
    HrRecord * record = nil;
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"HrRecord"];
    request.predicate = [NSPredicate predicateWithFormat:@"title = %@", title];
    NSSortDescriptor * sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"title" ascending:YES];
    request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    NSError * error = nil;
    NSArray * records = [context executeFetchRequest:request error:&error];

    if (!records || records.count > 1) {
        // Nil, or more than one is an error
    } else if (records.count == 0) {
        // Create a new record with starting duration of 0
        record = [NSEntityDescription insertNewObjectForEntityForName:@"HrRecord" inManagedObjectContext:context];
        record.title = title;
        record.duration = @0.0;
        record.distance = @0.0;
        record.date = [NSDate date];
    } else { // Recrod exists, exactly one
        record = [records lastObject];
        // update duration
        record.duration = @([record.duration intValue] + 1);
    }

    return record;
}
4

1 回答 1

0

您使用什么托管对象上下文？您应该使用在当前线程中创建的上下文。

于 2013-10-21T09:28:22.960 回答