这里的第一个问题,我尝试了很多东西,但无法弄清楚。
具有 2 个实体的核心数据,双向关系
A<<---->>B
A
实体具有名称作为属性和关系Bs
第一个控制器列出了所有A
实体,我有第二个控制器来添加A
实体,我想让它B
在其关系中保存一个默认值。
在为 segue 做准备时,我有以下代码:
if ([[segue identifier] isEqualToString:@"addAEntitySegue"]) {
AddAEntityViewController *addAEntityViewController = [segue destinationViewController];
addAEntityViewController.delegate = self;
addAEntityViewController.managedObjectContext = self.managedObjectContext;
NSManagedObjectContext *addingContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
self.addingManagedObjectContext = addingContext;
[addingManagedObjectContext setPersistentStoreCoordinator:[[fetchedResultsController managedObjectContext] persistentStoreCoordinator]];
addAEntityViewController.A = [NSEntityDescription insertNewObjectForEntityForName:@"A" inManagedObjectContext:addingContext];
UIBarButtonItem *saveButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSave
target:addAEntityViewController
action:@selector(save:)];
addAEntityViewController.navigationItem.rightBarButtonItem = saveButton;
}
在 addAEntityViewController 我有这个要保存
-(IBAction)save:(id)sender
{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"B" inManagedObjectContext:self.managedObjectContext];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == %@",[defaults objectForKey:@"BDefault"]];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:predicate];
//Set the batch size to a suitable number
[fetchRequest setFetchBatchSize:20];
NSError *error;
self.A.name = textFieldVal;
[self.A addBObject:[[self.managedObjectContext executeFetchRequest:fetchRequest error:&error] objectAtIndex:0]];
NSLog(@"A = %@", self.A.Bs);
[self.delegate addAEntityViewController:self didFinishWithSave:YES];
}
在addAEntityViewController
一切都正确保存的情况下,即使NSLog(@"A = %@", self.A.Bs);
语句显示B
. 但是当委托保存在第一个控制器(AEntityViewController
)中时,它只保存了关系,A.name
但不保存关系A.Bs
,我不知道出了什么问题。
这是委托方法:
-(void) addAEntityViewController:self didFinishWithSave:YES{
if (save) {
NSLog(@"saveworkouts");
NSError *error;
if (![addingManagedObjectContext save:&error]) {
// Update to handle the error appropriately.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
exit(-1); // Fail
}
}
// release the adding managed object context
self.addingManagedObjectContext = nil;
}
就像我说的那样,它保存A
实体而不是关系,B
即使关系B
正确保存在addAEntityViewController
(第二个视图)中。NSLOg
ofA.Bs
为空。