获取与NSFetchedResultsController有关系的对象

Question

这是我的问题：

我有2个实体：

• Session （日期，字符串名称，NSSet行为）

• Behaviour （字符串类别，字符串时间，字符串名称，NSManagedobject会话）。

他们是一对多的关系。

在SessioneViewController ，我获取Session和Behaviour ：

// This is for the fetch request
@property (nonatomic, ratain) NSArray *sessionArray; 

// Here I create the Session Object

Session *newSession = [NSEntityDescription insertNewObjectForEntityForName:@"Session"    inManagedObjectContext:self.managedObjectContext];
newSession.name = self.lblName.text;
newSession.date = [NSDate date];
self.managedObjectContext save:nil];
// I add the Session into the Array
self.sessionsArray = [self.sessionsArray arrayByAddingObject:newSession];

// Here I create the Behaviour Object:
Comportamento *newBehaviour = [NSEntityDescription   insertNewObjectForEntityForName:@"Behaviour" inManagedObjectContext:self.managedObjectContext];     
newBehaviour.name = cell.textLabel.text;
newBehaviour.category = @"Relationship";
newBehaviour.time = _lblTimer.text;

// Here I say which Session is part of the Behaviour
// --- EDIT ---
// Error Code: newBehaviour.session = [self.sessionsArray objectAtIndex:indexPath.row];
newBehaviour.session = [self.sessionsArray lastObject];

然后，我有两个视图控制器类，其中要显示Session ，然后在选择Session时需要相关的Behaviour 。

// In "ArchiveSessionVC.h":
@property (nonatomic, strong) NSFetchedResultsController *frs;
// In "ArchiveSessionVC.m":

- (void) viwDidLoad
{
   if(![[self frs] performFetch:&e]) {
    NSLog(@"Error %@", e);
    abort();
}


-(NSFetchedResultsController *)frs {
if (_frs != nil) {
    return _frs;
}
   NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
   NSEntityDescription *entity = [NSEntityDescription entityForName:@"Session" inManagedObjectContext:self.managedObjectContext];
   [fetchRequest setEntity:entity];

   NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"date"
                                                               ascending:NO];
   NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
   [fetchRequest setSortDescriptors:sortDescriptors];

   _frs = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];

    return _fetchedResultControllerSessions; 
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
       static NSString *CellIdentifier = @"SessioneCell";

       UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
       if (cell == nil) {
            cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault  reuseIdentifier:CellIdentifier];
        }

        Sessione *sessione = [self.fetchedResultControllerSessions      objectAtIndexPath:indexPath];
        cell.textLabel.text = sessione.nome;

        return cell;
}

在这里，我按下第二个视图控制器以显示Behaviuor ：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
      // Push del ViewController dei comportamenti:

      ArchiveBehaviuorsVC *aBehavioursVC =   [[ArchiveBehaviuorsVC alloc]   initWithNibName:@"ArchiveBehaviuorsVC" bundle:nil];
      aBehavioursVC.sessioneSelezionata = [self.fetchedResultControllerSessions     objectAtIndexPath:indexPath];
      [self.navigationController pushViewController:aBehavioursVC animated:YES];
}

我的ArchiveBehaviuorsVC是这样的：

 //"ArchiveBehaviuorsVC.h"
 @property (nonatomic, strong) Session *selectedSession;

 -(NSFetchedResultsController *)fetchedResultControllerBehaviours
 {
    if (_fetchedResultControllerBehaviours != nil) {
    return _fetchedResultControllerBehaviours;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Behaviour" inManagedObjectContext:self.managedObjectContext];
    //NSPredicate *predicate = [NSPredicate predicateWithFormat:@"session == %@",self.sessioneSelezionata];
    [fetchRequest setEntity:entity];
    [fetchRequest setPredicate:predicate];


    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"nome"
                                                               ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];

    _fetchedResultControllerBehaviours = [[NSFetchedResultsController alloc]   initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext   sectionNameKeyPath:nil cacheName:nil];


    return _fetchedResultControllerBehaviours;
 }

这是代码的一部分，但不起作用。 如何告诉fetchedResultzController仅显示与Session关联的Behaviour ？

-编辑-

我发现了问题，这不是NSPredicate错误，问题出在这一行代码中：

//错误代码：newBehaviour.session = [self.sessionsArray objectAtIndex：indexPath.row];

//正确的代码：

newBehaviour.session = [self.sessionsArray lastObject];

Answer 1

谓词

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"session == %@",self.sessioneSelezionata];

对我来说还不错。 您确定自己的行为错误吗？ 您是否尝试启用S​​QL调试 ？

-com.apple.CoreData.SQLDebug X

其中X可以是1,2或3。值越高，SQL输出越多。

此外，执行save 始终会传递错误参考。

NSError* error = nil;
[context save:&error];

上面的代码段返回布尔值，因此请检查它。 如果返回NO则打印错误。