objective-c - 获取一对多核心数据关系第一次返回正确的对象，但其他时间返回空集

Question

我有一个对象 Workout，它与一个对象 Exercise 具有一对多关系。

模型图:http://i.imgur.com/q1Mfq.png

当我创建一个 Workout 对象时，我通过循环将三个 Exercise 对象添加到它

[self addExercisesObject:exercise]

然后保存我的托管对象上下文。然后，从用于显示锻炼的 Controller 中，我可以成功获取锻炼及其练习(使用获取请求)，如我的调试器中的输出所示:

Printing description of self->_savedWorkout:
<Workout: 0x6c5a990> (entity: Workout; id: 0x6e46e00 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/Workout/p1> ; data: {
bodyweight = nil;
date = "2012-05-09 16:59:43 +0000";
exercises =     (
    "0x6e3c870 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/Exercise/p3>",
    "0x6e3eaf0 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/Exercise/p2>",
    "0x6e36820 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/Exercise/p1>"
);
isCompleted = 0;
workoutId = 1;
workoutPlan = "0x6e6c980 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/WorkoutPlan/p1>";
})

到目前为止一切顺利。但是，如果我在我的模拟器中关闭我的应用程序并再次启动它并在同一 View 中执行相同的获取请求，则锻炼看起来像这样:

Printing description of self->_savedWorkout:
<Workout: 0x6ea8ff0> (entity: Workout; id: 0x6e8f9e0 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/Workout/p1> ; data: {
bodyweight = nil;
date = "2012-05-09 16:59:43 +0000";
exercises =     (
);
isCompleted = 0;
workoutId = 1;
workoutPlan = "0x6c8a130 <x-coredata://EA417EAA-101A-4F04-8276-3C4A6CDF094D/WorkoutPlan/p1>";
})

它似乎获取了相同的锻炼对象，但现在锻炼是一个空集。实际上，在获取请求之后，练习首先看起来像这样:

exercises = "<relationship fault: 0x8a93100 'exercises'>";

但是一旦我这样做了:

for (Exercise *exercise in self.savedWorkout.exercises)

self.savedWorkout.exercises 解析为空集。我不会在我的应用程序的任何部分以任何方式编辑锻炼。

我的获取请求是通过我的 Workout 类中的此方法发出的:

- (Workout *)getLatestWorkout
{
  self.model = [[self.managedObjectContext persistentStoreCoordinator] managedObjectModel];

  NSFetchRequest *fetchRequest = [self.model fetchRequestTemplateForName:@"getLatestWorkout"];

  NSError *error = nil;
  NSArray *results = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
  if ([results count] == 1) {
    return [results objectAtIndex:0];
  }
  return nil;
}

我使用 Xcode 的 GUI 工具制作了获取请求模板。它在 isCompleted == 0 处获取所有 Workout 对象。您可以看到它每次都获取相同的对象，因为锻炼的 x-coredata 路径在两个调试器输出中是相同的。

更新:我检查了我的 SQLite 数据库。锻炼表中有一项锻炼，练习表中有三项练习。

有什么想法吗？

编辑:创建下面发布的对象的代码

<p></p>

<pre><code>- (void)storeUserSettings
{
  // get the file path if it exists
  NSString *path = [[NSBundle mainBundle] pathForResource:@"userSettings" ofType:@"plist"];

  // create it if it doesn't
  if (path == nil) {
    path = [NSString stringWithFormat:@"%@%@", 
            [[NSBundle mainBundle] bundlePath], @"/userSettings.plist"];
  }

  // and write the new settings to file
  [self.userSettings writeToFile:path atomically:YES];

  // load managed object context
  [self loadMOC];

  WorkoutPlan *currentPlan = [[WorkoutPlan alloc] getActiveWorkoutPlan];

  [currentPlan setManagedObjectContext:self.managedObjectContext];

  // if user has no plan or is changing plans, create new plan and first workout
  if (currentPlan == nil || 
      ([self.userSettings valueForKey:@"plan"] != currentPlan.planId)) {

    // create a workoutPlan object
    WorkoutPlan *workoutPlan = [[WorkoutPlan alloc] initWithEntity:
                                [NSEntityDescription entityForName:@"WorkoutPlan" 
                                            inManagedObjectContext:self.managedObjectContext] 
                                    insertIntoManagedObjectContext:self.managedObjectContext];

    // set attributes to values from userSettings and save object
    [workoutPlan createWorkoutPlanWithId:[self.userSettings valueForKey:@"plan"] 
                                schedule:[self.userSettings valueForKey:@"schedule"]
                             dateStarted:[self.userSettings valueForKey:@"nextDate"]];
  }
  // if user is just changing schedule, update schedule of current plan
  else if (![currentPlan.schedule isEqualToString:[self.userSettings valueForKey:@"schedule"]]) {
    [currentPlan setSchedule:[self.userSettings valueForKey:@"schedule"]];

    [currentPlan saveMOC];
  }
}

- (void)loadMOC
{
  AppDelegate *delegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];
  self.managedObjectContext = delegate.managedObjectContext;
  self.model = [[self.managedObjectContext persistentStoreCoordinator] managedObjectModel];
}

- (void)createWorkoutPlanWithId:(NSNumber *)planId schedule:(NSString *)schedule 
                    dateStarted:(NSDate *)dateStarted
{ 
  [self deactivateCurrentPlan];

  // set workout plan attributes
  [self setPlanId:planId];
  [self setIsActive:[NSNumber numberWithBool:YES]];
  [self setSchedule:schedule];
  [self setDateStarted:dateStarted]; 

  // create first workout and add to workout plan

  Workout *firstWorkout = [NSEntityDescription
                          insertNewObjectForEntityForName:@"Workout"
                          inManagedObjectContext:self.managedObjectContext];

  [firstWorkout setManagedObjectContext:self.managedObjectContext];

  [firstWorkout createFirstWorkoutForPlan:self onDate:dateStarted];

  [self addWorkoutsObject:firstWorkout];

  [self saveMOC];
}

- (void)createFirstWorkoutForPlan:(WorkoutPlan *)plan onDate:(NSDate *)startDate
{
  // set workout attributes
  [self setDate:startDate];
  [self setIsCompleted:[NSNumber numberWithBool:NO]];
  [self setWorkoutId:[NSNumber numberWithInt:1]];

  NSArray *exerciseList = [self getExercisesForWorkout:self inPlan:plan];

  // iterate over exercises in spec and create them
  for (NSDictionary *exerciseSpec in exerciseList) 
  {
    // create a exercise MO
    Exercise *exercise = [NSEntityDescription
                          insertNewObjectForEntityForName:@"Exercise"
                          inManagedObjectContext:[plan managedObjectContext]];

    [exercise setManagedObjectContext:[plan managedObjectContext]];
    [exercise createExerciseForWorkout:self withSpec:exerciseSpec];

    // add exercise to workout object
    [self addExercisesObject:exercise];
  }

}

- (void)createExerciseForWorkout:(Workout *)workout withSpec:exerciseSpec
{
  // set exercise attributes
  self.exerciseId = [exerciseSpec valueForKey:@"id"];
  self.isPersonalRecord = [NSNumber numberWithBool:NO];

  NSArray *sets = [exerciseSpec valueForKey:@"sets"];
  int i = 1;
  for (NSNumber *setReps in sets)
  {
    // create a set MO
    Set *set = [NSEntityDescription
                          insertNewObjectForEntityForName:@"Set"
                          inManagedObjectContext:[workout managedObjectContext]];

    [set setManagedObjectContext:[workout managedObjectContext]];

    // set set attributes
    set.order = [NSNumber numberWithInt:i];
    set.repetitions = setReps;
    set.weight = [exerciseSpec valueForKey:@"default_weight"]; 

    // add set to exercise object
    [self addSetsObject:set];
    i++;
  }
}
</code></pre>

<p></p>

Answer 1

我遇到了类似的问题。父子关系在应用程序运行时有效，但在重新启动后仅检索到最新的子记录。

我是这样添加 child 的:

• 创建子记录
• 设置 child 的parent属性，设置 child 的other属性
• 使用父级的添加方法将子级添加到父级

我发现如果我这样做是固定的:

• 创建子记录
• 使用父级的添加方法将子级添加到父级
• 设置 child 的parent属性，设置 child 的other属性