Question

我的核心数据中有2个托管对象：CoreDataTrap＆amp; CoreDataAllTraps。到目前为止，有关CoreDataTrap的更新，添加，删除，保存等方面的一切进展顺利。但是，当我尝试使用第二个托管对象CoreDataAllTraps时，我没有错误的描述，只是一个简单的nil数组获取对象。

弄乱CoreDataAllTraps：

的示例

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:kCORE_DATA_ALL_TRAPS_ENTITY inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    NSError *error = nil;
    NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    if (fetchedObjects == nil || fetchedObjects.count == 0) {
        NSLog(@"localizedDescription: %@, userInfo: %@", error.localizedDescription, error.userInfo);
        success = NO;
    }


    NSLog(@"%s success/fail: %@", __PRETTY_FUNCTION__, success?@"yes":@"no");
    NSLog(@"fetchedObjects.count: %d", fetchedObjects.count);

记录下来：fetchedObjects.count：0

我记录了一个没有任何细节的错误，fetchedObjects.count=0。我尝试创建一个新的NSManagedObjectContext并从AppDelegate引用一个，但没有一个工作。

修改

首次将（在一个类中）对象添加到CoreDataAllTraps，因为我记录对象并查看详细信息是否正确。
我的情况是fetchedObjects.count = 0（在其他课程中）。

修改-2：

从不同的课程中保存（效果很好）：

- (void)addOrUpdateTrap:(Traps*)trapObject
{
    int trapID = trapObject.getTrapID;
    CoreDataAllTraps *trapEntity = nil;
    NSError *error = nil;

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:kCORE_DATA_ALL_TRAPS_ENTITY];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"trapID == %d", trapID];
    [fetchRequest setPredicate:predicate];

    NSArray *results = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    if (results == nil)
    {
        // Handle error
    }
    else if ([results count] == 0)
    {
        // Nothing to update, add new trap
        // Create a new record (row)
        trapEntity = [NSEntityDescription insertNewObjectForEntityForName:kCORE_DATA_ALL_TRAPS_ENTITY inManagedObjectContext:self.managedObjectContext];
    }
    else
    {
        trapEntity = results[0]; // There should be only one object for the ID.
    }


    if (trapEntity != nil)
    {
        // Set properties for new or existing object ...

        // Int
        [trapEntity setTrapID:[NSNumber numberWithInt:trapObject.getTrapID]];
        [trapEntity setType:[NSNumber numberWithInt:trapObject.getTrapType]];
        [trapEntity setDist:[NSNumber numberWithInt:trapObject.getTrapDistanceToCar]];
        [trapEntity setDist_to_close_point:[NSNumber numberWithInt:trapObject.getTrapDistanceToClosePoint]];
        [trapEntity setActive:[NSNumber numberWithInt:trapObject.isActive]];
        [trapEntity setAlert:[NSNumber numberWithInt:trapObject.isAlert]];
        [trapEntity setAlarmDistance:[NSNumber numberWithInt:trapObject.alarmDistance]];
        [trapEntity setRoadNumber:[NSNumber numberWithInt:trapObject.roadNumber]];
        [trapEntity setPolys:[NSNumber numberWithInt:trapObject.polygons]];
        [trapEntity setEnter_to_area:[NSNumber numberWithInt:trapObject.getTrapEnterToArea]];

        // Double
        [trapEntity setLat:[NSNumber numberWithDouble:trapObject.getTrapLat]];
        [trapEntity setLon:[NSNumber numberWithDouble:trapObject.getTrapLon]];
        [trapEntity setClose_point_lat:[NSNumber numberWithDouble:trapObject.getTrapClosePointLat]];
        [trapEntity setClose_point_lon:[NSNumber numberWithDouble:trapObject.getTrapClosePointLon]];

        // NSString
        [trapEntity setLastTrapAlarm:[NSString stringWithFormat:@"%li", trapObject.getTrapLastAlarm]];
        [trapEntity setPoly0:trapObject.getTrapPolygonA];
        [trapEntity setPoly1: trapObject.getTrapPolygonB];
        [trapEntity setPoly2: trapObject.getTrapPolygonC];
        [trapEntity setPolygonAzimut1: trapObject.getTrapPolygonAzimuthA];
        [trapEntity setPolygonAzimut2: trapObject.getTrapPolygonAzimuthB];
        [trapEntity setPolygonAzimut3: trapObject.getTrapPolygonAzimuthC];
        [trapEntity setDesc: trapObject.getTrapDesc];
        // etc. for all properties ...

        error = nil;
        if ([self.managedObjectContext save:&error] == NO)
        {
            NSLog(@"%s error saving: %@\n%@", __PRETTY_FUNCTION__, error.localizedDescription, error.userInfo);
        }
    }
}

然后从不同的班级阅读，以确保一切正常（效果很好）：

- (void)saveArray
{
    // [Netroads sharedInstance].arrayOfAllTraps = [dbat getAllTraps];
    [Netroads sharedInstance].arrayOfAllTraps = self.allTraps;
    NSLog(@"[Netroads sharedInstance].arrayOfAllTraps.count: %i", [Netroads sharedInstance].arrayOfAllTraps.count);

    self.managedObjectContext = appDelegate.managedObjectContext;
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:kCORE_DATA_ALL_TRAPS_ENTITY inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];
    NSError *error = nil;
    NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    NSLog(@"fetchedObjects.count: %d", fetchedObjects.count);

记录下来：

fetchedObjects.count: 222

UPDATE-1：

我尝试了其他的东西：当我将对象保存到核心数据时，我从原始保存功能的末尾调用该函数。这种方式看起来很糟糕，但它确实有效。我仍然在寻找一种美妙的方式来混淆MOC而不需要在不同函数的末尾调用函数。

fetchedObjects（NSArray）计数在它满了对象时返回0

0 个答案: