Core Data 中保存/获取数据的不一致

Question

我在这里的第一篇文章，直奔主题。

我遇到了一个问题，我不确定是保存数据还是获取数据。 这是我尝试将数据保存在我的实体“序列”中的代码。该实体由 2 个属性“seqForWk1CD”和“seqForWk2CD”组成。

AppDelegate *delegate = [[UIApplication sharedApplication]delegate];
NSManagedObjectContext *context = [delegate managedObjectContext];
SequenceMO *seqEntity = [NSEntityDescription 
insertNewObjectForEntityForName:@"Sequence" 
inManagedObjectContext:context];
// some other code
seqEntity.seqForWk1CD = arrForWk1;
seqEntity.seqForWk2CD = arrForWk2;
NSLog(@"%@", arrForWk1);
NSLog(@"%@", arrForWk2);
NSError *error = nil;
if (context != nil) {
    if ([context hasChanges] && ![context save:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }

打印时，数组将始终显示数组的内容。

这是我尝试获取数据的地方。

AppDelegate *delegate = [[UIApplication sharedApplication]delegate];
NSManagedObjectContext *context = [delegate managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc]init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Sequence" inManagedObjectContext:context];
[request setEntity:entity];
NSError *error;
if(![context save:&error]){
    NSLog(@"Error fetching. %@ %@", error, [error localizedDescription]);
}
NSUInteger count = [context countForFetchRequest:request error:&error];
if(count != 0){
    NSArray *fetchObj = [context executeFetchRequest:request error:&error];
    NSManagedObject *sequence = (NSManagedObject *)[fetchObj objectAtIndex:0];
    NSLog(@"1 - %@", sequence);
    arrForWk1 = [sequence valueForKey:@"seqForWk1CD"];
    NSLog(@"%@", arrForWk1);
    arrForWk2 = [sequence valueForKey:@"seqForWk2CD"];
    NSLog(@"%@", arrForWk2);
}

当我重新启动应用程序时出现问题。数组要么显示（空）两个数组，要么显示两个数组的内容。 if(![context save:&error]) 的 if 语句永远不会被触发。已经为实体添加了 NSManagedObject 的子类。

我也尝试在@interface 中声明 AppDelegate 并通过 [delegate saveContext]; 强制立即保存上下文。

这是进行保存的方法。 "check" 在 vi​​ewDidLoad 方法中被初始化为 0。 “arrForWk1”和“arrForWk2”都在@interface 声明。

- (IBAction)randomizeSequence:(UIButton *)sender { 
   NSMutableArray *storeArray = [[NSMutableArray alloc] init];
   AppDelegate *delegate = [[UIApplication sharedApplication]delegate];
   NSManagedObjectContext *context = [delegate managedObjectContext];
   SequenceMO *seqEntity = [NSEntityDescription insertNewObjectForEntityForName:@"Sequence" inManagedObjectContext:context];
   BOOL record = NO;
   int x;

   for (int i=0; [storeArray count] < 9; i++) //Loop for generate different random values
    {
       x = 1 + arc4random() % 9;//generating random number
       if(i==0)//for first time
       {
        [storeArray addObject:[NSNumber numberWithInt:x]];
       }
       else
       {
          for (int j=0; j<= [storeArray count]-1; j++)
          {
              if (x ==[[storeArray objectAtIndex:j] intValue])
                  record = YES;
          }

          if (record == YES)
          {
              record = NO;
          }
          else
          {
              [storeArray addObject:[NSNumber numberWithInt:x]];
          }
       }
    }
    check++;
    if(check == 1 ) {
       arrForWk1 = storeArray;
       [self.wk1Seq reloadData];
    }
    else if(check == 2) {
        arrForWk2 = storeArray;
        seqEntity.seqForWk1CD = arrForWk1;
        seqEntity.seqForWk2CD = arrForWk2;
        NSError *error = nil;
        if (context != nil) {
            if ([context hasChanges] && ![context save:&error]) {
                NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
                abort();
            }
        }

        [self.wk2Seq reloadData];
}

补充一点，数组的数据类型是 NSMutableArray，我正在尝试将它们存储到“Transformable”类型的属性中。

Answer 1

经过研究，我设法解决了这个问题。我不确定它实际上是如何工作的，但我在尝试获取数据时通过重新排列代码来解决它。

AppDelegate *delegate = [[UIApplication sharedApplication]delegate];
NSManagedObjectContext *context = [delegate managedObjectContext];
NSEntityDescription *descriptor = [NSEntityDescription entityForName:@"Sequence" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc]init];
request.entity = descriptor;
NSError *error;
NSArray *fetchObj = [context executeFetchRequest:request error:&error];
if(fetchObj == nil) {
    NSLog(@"Error occured when trying to fetch.");

}
else {
    if(fetchObj.count == 0) {
        NSLog(@"No objects saved");
    else {
        NSManagedObject *sequence = (NSManagedObject *)[fetchObj objectAtIndex:0];
        NSLog(@"1 - %@", sequence);
        arrForWk1 = [sequence valueForKey:@"seqForWk1CD"];
        NSLog(@"%@", arrForWk1);
        arrForWk2 = [sequence valueForKey:@"seqForWk2CD"];
        NSLog(@"%@", arrForWk2);
        NSLog(@"2 - %@", sequence);
    } 

我也试过两种保存数据的方法。在我尝试保存数据的if statement 中，我将NSMutableArrays 转换为NSArrays。

else if(check == 2) {
    test2 = storeArray;
    NSManagedObjectContext *context = [delegate managedObjectContext];
    SequenceMO *seqEntity = [NSEntityDescription insertNewObjectForEntityForName:@"Sequence" inManagedObjectContext:context];
    NSArray *tArr = [arrForWk1 copy];
    NSArray *tArr2 = [arrForWk2 copy];
    seqEntity.seqForWk1CD = tArr;
    seqEntity.seqForWk2CD = tArr2;
    NSError *error = nil;
    if (context != nil) {
        if ([context hasChanges] && ![context save:&error]) {
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }

我尝试的第二种方法是使用Core Data not saving changes to Transformable property的答案

id temp = [seqEntity seqForWk1CD];
id temp2 = [seqEntity seqForWk2CD];
temp = arrForWk1;
temp2 = arrForWk2;
[seqEntity setSeqForWk1CD:temp];
[seqEntity setSeqForWk2CD:temp2];

显然它以某种方式起作用。