objective-c - 核心数据 NSManagedObject isFault insideprepareForDeletion

Question

我正在- prepareForDeletion里面做一些处理在 NSManagedObject 。但是，当我尝试访问此类的某些属性时，它们将作为 nil 返回给我。 (尽管我知道它们不是 nil )。所以我检查我的对象是否有故障 [self isFault]它返回 YES 。

那么，当我在里面时，如何才能使该对象“没有故障”- prepareForDeletion因为我需要访问属性？

PhoneGroup.m(NSManagedObject)

- (void)prepareForDeletion {

    [super prepareForDeletion];

    NSArray *individuals = [self.individuals allObjects]; // individuals is nil

    for (int i = 0; i < [individuals count]; i++) {

        Individual *individual = [individuals objectAtIndex:i];

        BOOL individualExistsInOtherGroups = [individual.phoneGroups count] > 1;

        BOOL individualAddedAsAdditionalContactToReminder = [individual.reminders count] > 0;

        // We can delete the individual if individual does not exist in other groups and is not added to any reminders

        if (!individualExistsInOtherGroups && !individualAddedAsAdditionalContactToReminder && ![individual isDeleted]) {

            [[CoreDataHelper sharedInstance] deleteEntity:individual inManagedObjectContext:self.managedObjectContext];
        }
    }

    // Post a notification to notify all interested VC so they can refresh the GUI
    [[NSNotificationCenter defaultCenter] postNotificationName:RMContactDeletedNotification object:self];
    DLog(@"Contact deleted notification sent");
}

型号信息:

PhoneGroup与 Individual 具有逆对多关系删除规则无效。

Individual与 PhoneGroup 具有逆对多关系删除规则无效。

Contact是 Individual 的父类(super class)和 PhoneGroup

这是一个可以更好地可视化的图像。

编辑:我对此问题有了更多发现

PhoneGroup仅当与 Reminder 有关系时才会出现故障。如果 PhoneGroup与 Reminder 没有关系当它被删除时，这不是错误。

Reminder与 Contact 具有可选的逆对多关系删除规则无效。

Contact与 Reminder 具有可选的逆对多关系删除规则无效。

这有什么好处？

编辑 2:有关该问题的更多发现

我尝试了 Dan Shelly 的替代解决方案来获取 Individual 然而甚至是 self.managedObjectContext NSManagedObject的( PhoneGroup ) 是 nil里面- prepareForDeletion这意味着什么？

Answer 1

Why does [self.individuals allObjects] return nil?

编辑:
发现你的managedObjectContext后是 nil可以肯定地说，您的对象已被其上下文所否认。
这可能是由上下文 reset 引起的或释放，同时保持对对象的强引用。
然而，这并不能解释这是如何在 prepareForDeletion 内发生的。方法。
当事件上下文正在删除对象 ( [context deleteObject:...] ) 时，会调用此方法。
这意味着您要么调用 prepareForDeletion手动( [object prepareForDeletion] )，或者另一个线程正在删除中间重置/解除分配您的上下文。

Note: The below code will work given that you have a valid objectID and a live managedObjectContext set on your object.

但是，我可能有一个解决方法，因为您访问数据的方式有些低效(稍后会解释):

如果您删除的对象 ( PhoneGroup ) individuals关系没有故障，CoreData 将首先访问存储来故障关系(第一趟)。然后，您将出现错误，因为该关系中包含的对象(N 个对象)，您的循环将一一访问它们(N 次到商店)。仍然在循环中，您可以访问每个对象的关系(2 个关系船， phoneGroups 和 reminders ==> 每个项目 2 次到商店)。
总之:1 + N + 2*N = 3*N +1 次去商店(最坏情况)。

这可以通过更简单的方式来完成:
* 创建此获取请求:

NSFetchRequest* r = [[NSFetchRequest alloc] initWithEntityName:@"Individual"];
[r setPredicate:[NSPredicate predicateWithFormat:@"%@ IN phoneGroups AND phoneGroups.@count == 1 AND reminders.@count == 0",[self objectID]]];
[r setIncludesPropertyValues:YES];
[r setReturnsObjectsAsFaults:NO];
[r setIncludesPendingChanges:YES];

* 现在剩下的就是:

NSManagedObjectContext* context = [self managedObjectContext];
NSArray* individuals = [context executeFetchRequest:r error:NULL];    
for (Individual* individual in individuals) {
    [context deleteObject:individual];
}

在最坏的情况下，这只需前往商店一次 (1) 次即可完成，并且由于您不直接依赖于您的关系，因此只要您的对象具有其 objectID ，这就应该有效。 .

附录:

当前实现性能(SQLite 调试):

//2013-05-19 21:34:42.700 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM Z_2PHONEGROUPS t1 JOIN ZCONTACT t0 ON t0.Z_PK = t1.Z_2INDIVIDUALS WHERE t1.Z_3PHONEGROUPS = ?
//2013-05-19 21:34:42.701 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.701 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 3 rows.
//2013-05-19 21:34:42.715 P[9666:c07] CoreData: annotation: to-many relationship fault "individuals" for objectID 0x8572b70 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/PhoneGroup/p21> fulfilled from database.  Got 3 rows
//2013-05-19 21:34:42.716 P[9666:c07] CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.Z_OPT, t0.ZNAME, t0.ZCONTACTID, t0.ZVISIBLE FROM ZCONTACT t0 WHERE  t0.Z_PK = ?
//2013-05-19 21:34:42.717 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0005s
//2013-05-19 21:34:42.717 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 1 rows.
//2013-05-19 21:34:42.718 P[9666:c07] CoreData: annotation: fault fulfilled from database for : 0x818cad0 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p4>
//2013-05-19 21:34:42.718 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM Z_2PHONEGROUPS t1 JOIN ZCONTACT t0 ON t0.Z_PK = t1.Z_3PHONEGROUPS WHERE t1.Z_2INDIVIDUALS = ?
//2013-05-19 21:34:42.719 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.719 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 1 rows.
//2013-05-19 21:34:42.719 P[9666:c07] CoreData: annotation: to-many relationship fault "phoneGroups" for objectID 0x818cad0 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p4> fulfilled from database.  Got 1 rows
//2013-05-19 21:34:42.720 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM ZREMINDER t0 WHERE  t0.ZCONTACT = ?
//2013-05-19 21:34:42.721 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0005s
//2013-05-19 21:34:42.721 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 0 rows.
//2013-05-19 21:34:42.721 P[9666:c07] CoreData: annotation: to-many relationship fault "reminders" for objectID 0x818cad0 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p4> fulfilled from database.  Got 0 rows
//2013-05-19 21:34:42.722 P[9666:c07] CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.Z_OPT, t0.ZNAME, t0.ZCONTACTID, t0.ZVISIBLE FROM ZCONTACT t0 WHERE  t0.Z_PK = ?
//2013-05-19 21:34:42.722 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.722 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 1 rows.
//2013-05-19 21:34:42.723 P[9666:c07] CoreData: annotation: fault fulfilled from database for : 0x818cb90 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p16>
//2013-05-19 21:34:42.723 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM Z_2PHONEGROUPS t1 JOIN ZCONTACT t0 ON t0.Z_PK = t1.Z_3PHONEGROUPS WHERE t1.Z_2INDIVIDUALS = ?
//2013-05-19 21:34:42.724 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.724 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 1 rows.
//2013-05-19 21:34:42.724 P[9666:c07] CoreData: annotation: to-many relationship fault "phoneGroups" for objectID 0x818cb90 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p16> fulfilled from database.  Got 1 rows
//2013-05-19 21:34:42.725 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM ZREMINDER t0 WHERE  t0.ZCONTACT = ?
//2013-05-19 21:34:42.725 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.726 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 0 rows.
//2013-05-19 21:34:42.726 P[9666:c07] CoreData: annotation: to-many relationship fault "reminders" for objectID 0x818cb90 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p16> fulfilled from database.  Got 0 rows
//2013-05-19 21:34:42.727 P[9666:c07] CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.Z_OPT, t0.ZNAME, t0.ZCONTACTID, t0.ZVISIBLE FROM ZCONTACT t0 WHERE  t0.Z_PK = ?
//2013-05-19 21:34:42.727 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.727 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 1 rows.
//2013-05-19 21:34:42.728 P[9666:c07] CoreData: annotation: fault fulfilled from database for : 0x818cba0 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p17>
//2013-05-19 21:34:42.728 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM Z_2PHONEGROUPS t1 JOIN ZCONTACT t0 ON t0.Z_PK = t1.Z_3PHONEGROUPS WHERE t1.Z_2INDIVIDUALS = ?
//2013-05-19 21:34:42.729 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.729 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0008s for 4 rows.
//2013-05-19 21:34:42.729 P[9666:c07] CoreData: annotation: to-many relationship fault "phoneGroups" for objectID 0x818cba0 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p17> fulfilled from database.  Got 4 rows
//2013-05-19 21:34:42.730 P[9666:c07] CoreData: sql: SELECT 0, t0.Z_PK FROM ZREMINDER t0 WHERE  t0.ZCONTACT = ?
//2013-05-19 21:34:42.730 P[9666:c07] CoreData: annotation: sql connection fetch time: 0.0004s
//2013-05-19 21:34:42.731 P[9666:c07] CoreData: annotation: total fetch execution time: 0.0007s for 0 rows.
//2013-05-19 21:34:42.731 P[9666:c07] CoreData: annotation: to-many relationship fault "reminders" for objectID 0x818cba0 <x-coredata://CBE585F2-552D-4FDE-AAEA-2C9C7984FAC9/Individual/p17> fulfilled from database.  Got 0 rows

建议的实现性能:

//2013-05-19 21:13:26.734 P[9609:c07] CoreData: sql: SELECT t0.Z_ENT, t0.Z_PK, t0.Z_OPT, t0.ZNAME, t0.ZCONTACTID, t0.ZVISIBLE FROM ZCONTACT t0 JOIN Z_2PHONEGROUPS t1 ON t0.Z_PK = t1.Z_2INDIVIDUALS WHERE ((t1.Z_3PHONEGROUPS = ? AND (SELECT COUNT(t3.Z_3PHONEGROUPS) FROM Z_2PHONEGROUPS t3 WHERE (t0.Z_PK = t3.Z_2INDIVIDUALS) ) = ? AND (SELECT COUNT(t4.Z_PK) FROM ZREMINDER t4 WHERE (t0.Z_PK = t4.ZCONTACT) ) = ?) AND  t0.Z_ENT = ?)
//2013-05-19 21:13:26.735 P[9609:c07] CoreData: annotation: sql connection fetch time: 0.0008s
//2013-05-19 21:13:26.736 P[9609:c07] CoreData: annotation: total fetch execution time: 0.0012s for 2 rows.

数据构建( - (void) synthesizePhoneGroupsAndIndividuals:(NSManagedObjectContext*)context ):

NSMutableArray* individuals = [NSMutableArray new];//[NSEntityDescription insertNewObjectForEntityForName:@"Individual" inManagedObjectContext:context];
for (NSUInteger i = 0; i < (3 + arc4random() % 100); ++i) {
    Individual* indi = [NSEntityDescription insertNewObjectForEntityForName:@"Individual" inManagedObjectContext:context];
    indi.contactID = [NSString stringWithFormat:@"cid-%u",i];
    [individuals addObject:indi];
}

NSMutableArray* groups = [NSMutableArray new];
for (NSUInteger i = 0; i < 3 + arc4random() % 7; ++i) {
    PhoneGroup* group = [NSEntityDescription insertNewObjectForEntityForName:@"PhoneGroup" inManagedObjectContext:context];
    group.visible = NO;
    NSMutableSet* indis = [group mutableSetValueForKey:@"individuals"];
    for (NSUInteger j = 0; j < 3; ++j) {
        [indis addObject:[individuals objectAtIndex:(arc4random() % [individuals count])]];
    }
    [groups addObject:group];
}

[context save:NULL];

测试代码:

NSManagedObjectContext* context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
context.persistentStoreCoordinator = _persistentStoreCoordinator;

[context performBlockAndWait:^{
    [self synthesizePhoneGroupsAndIndividuals:context];
    [context reset];
}];

[context performBlockAndWait:^{
    NSFetchRequest* r = [[NSFetchRequest alloc] initWithEntityName:@"PhoneGroup"];
    NSArray* groups = [context executeFetchRequest:r error:NULL];
    if ([groups count]) {
        PhoneGroup* group = [groups objectAtIndex:(arc4random() % [groups count])];
        [context deleteObject:group];
    }
}];