如何在CoreData中将相关对象从一个对象移动到另一个

Question

我在CoreData中进行某些数据库操作时遇到麻烦。 有时，视图会在过程的中间刷新并显示错误的状态。 有时甚至会丢失数据。

我有以下CoreData对象模型：

课程有很多学生

现在，我想将两个课程A和B合并在一起，以便之后将课程B的所有学生分配到课程A，而课程B不再存在。

（一个学生正好上一门课程）

目前，我正在以这种方式进行操作，虽然大部分时间都可以使用，但存在上述问题：

Course courseA = [self someCourse];
Course courseB = [self someOtherCourse];

for (Student *student in courseB.students) {
    student.course = courseA;
}

[managedObjectContext deleteObject:courseB];

NSError *error = nil;
[managedObjectContext save:&error];
if(error != nil) {
    NSLog(@"Deletion of Course failed.");
}

有时我在设备日志中收到以下错误：

Core Data: warning: validation recovery attempt FAILED with Error Domain=NSCocoaErrorDomain Code=1550 "The operation couldn’t be completed. (Cocoa error 1550.)" UserInfo=0x1d97f8e0 {NSLocalizedDescription=The operation couldn’t be completed. (Cocoa error 1550.), Dangling reference to an invalid object.=null, NSValidationErrorObject=<Course: 0x1cad56c0> (entity: Course; id: 0x1ca69380 <x-coredata:///Course/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D3519> ; data: {
    endDateTime = "2014-09-18 17:38:17 +0000";
    place = "0x1db4c120 <x-coredata:///Place/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D7394>";
    room = "0x18d696a0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Room/p1>";
    category = "0x18e8f990 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/CDCategory/p1>";
    changed = "2014-09-19 08:04:03 +0000";
    startDateTime = "2014-09-18 17:30:01 +0000";
    syncInfos = "<relationship fault: 0x1cbb5bb0 'syncInfos'>";
    students =     (
        "0x18d073c0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461393>",
        "0x1c911b00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461383>",
        "0x1c915770 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461401>",
        "0x1a0a6560 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461387>",
        "0x1c90e2f0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461346>",
        "0x1cd7fc00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461370>",
        "0x1a0bdbf0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461374>",
        "0x1cb11090 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461395>",
        "0x1cf31fc0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461379>",
        "0x1cda6230 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461339>",
        "(...and 133 more...)"
    );
}), NSAffectedObjectsErrorKey=(
    "<Student: 0x1cf6c000> (entity: Student; id: 0x1a36fc70 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461431> ; data: <fault>)"
), NSValidationErrorKey=students, NSValidationErrorValue=Relationship 'students' on managed object (0x1cad56c0) <Course: 0x1cad56c0> (entity: Course; id: 0x1ca69380 <x-coredata:///Course/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D3519> ; data: {
    endDateTime = "2014-09-18 17:38:17 +0000";
    place = "0x1db4c120 <x-coredata:///Place/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D7394>";
    room = "0x18d696a0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Room/p1>";
    category = "0x18e8f990 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/CDCategory/p1>";
    changed = "2014-09-19 08:04:03 +0000";
    startDateTime = "2014-09-18 17:30:01 +0000";
    syncInfos = "<relationship fault: 0x1cbb5bb0 'syncInfos'>";
    students =     (
        "0x18d073c0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461393>",
        "0x1c911b00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461383>",
        "0x1c915770 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461401>",
        "0x1a0a6560 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461387>",
        "0x1c90e2f0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461346>",
        "0x1cd7fc00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461370>",
        "0x1a0bdbf0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461374>",
        "0x1cb11090 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461395>",
        "0x1cf31fc0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461379>",
        "0x1cda6230 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461339>",
        "(...and 133 more...)"
    );
}) with objects {(
    <Student: 0x1d9e48d0> (entity: Student; id: 0x18d073c0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461393> ; data: <fault>),
    <Student: 0x1ddc6920> (entity: Student; id: 0x1c911b00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461383> ; data: <fault>),
    <Student: 0x1d991750> (entity: Student; id: 0x1c915770 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461455> ; data: <fault>),
    <Student: 0x1cf6c000> (entity: Student; id: 0x1a36fc70 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461431> ; data: <fault>)
)}, NSValidationErrorShouldAttemptRecoveryKey=true} and {
    "Dangling reference to an invalid object." = "<null>";
    NSAffectedObjectsErrorKey =     (
        "<Student: 0x1cf6c000> (entity: Student; id: 0x1a36fc70 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461431> ; data: <fault>)"
    );
    NSLocalizedDescription = "The operation couldn\U2019t be completed. (Cocoa error 1550.)";
    NSValidationErrorKey = students;
    NSValidationErrorObject = "<Course: 0x1cad56c0> (entity: Course; id: 0x1ca69380 <x-coredata:///Course/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D3519> ; data: {\n    endDateTime = \"2014-09-18 17:38:17 +0000\";\n    place = \"0x1db4c120 <x-coredata:///Place/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D7394>\";\n    room = \"0x18d696a0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Room/p1>\";\n    category = \"0x18e8f990 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/CDCategory/p1>\";\n    changed = \"2014-09-19 08:04:03 +0000\";\n    startDateTime = \"2014-09-18 17:30:01 +0000\";\n    points = 1436;\n    done = 1;\n    notes = \"\";\n    syncInfos = \"<relationship fault: 0x1cbb5bb0 'syncInfos'>\";\n    students =     (\n        \"0x18d073c0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461393>\",\n        \"0x1c911b00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461383>\",\n        \"0x1c915770 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461401>\",\n        \"0x1a0a6560 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461387>\",\n        \"0x1c90e2f0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461346>\",\n        \"0x1cd7fc00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461370>\",\n        \"0x1a0bdbf0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461374>\",\n        \"0x1cb11090 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461395>\",\n        \"0x1cf31fc0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461379>\",\n        \"0x1cda6230 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461339>\",\n        \"(...and 133 more...)\"\n    );\n})";
    NSValidationErrorShouldAttemptRecoveryKey = 1;
    NSValidationErrorValue = "Relationship 'students' on managed object (0x1cad56c0) <Course: 0x1cad56c0> (entity: Course; id: 0x1ca69380 <x-coredata:///Course/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D3519> ; data: {\n    endDateTime = \"2014-09-18 17:38:17 +0000\";\n    place = \"0x1db4c120 <x-coredata:///Place/tA8FBABB4-2BBD-4A5D-ADFA-94D6F08F6A6D7394>\";\n    room = \"0x18d696a0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Room/p1>\";\n    category = \"0x18e8f990 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/CDCategory/p1>\";\n    changed = \"2014-09-19 08:04:03 +0000\";\n    startDateTime = \"2014-09-18 17:30:01 +0000\";\n    points = 1436;\n    done = 1;\n    notes = \"\";\n    syncInfos = \"<relationship fault: 0x1cbb5bb0 'syncInfos'>\";\n    students =     (\n        \"0x18d073c0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461393>\",\n        \"0x1c911b00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461383>\",\n        \"0x1c915770 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461401>\",\n        \"0x1a0a6560 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461387>\",\n        \"0x1c90e2f0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461346>\",\n        \"0x1cd7fc00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461370>\",\n        \"0x1a0bdbf0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461374>\",\n        \"0x1cb11090 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461395>\",\n        \"0x1cf31fc0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461379>\",\n        \"0x1cda6230 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461339>\",\n        \"(...and 133 more...)\"\n    );\n}) with objects {(\n    <Student: 0x1d9e48d0> (entity: Student; id: 0x18d073c0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461393> ; data: <fault>),\n    <Student: 0x1ddc6920> (entity: Student; id: 0x1c911b00 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461383> ; data: <fault>),\n    <Student: 0x1d991750> (entity: Student; id: 0x1c915770 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461433> ; data: <fault>),\n    <Student: 0x1dbb38f0> (entity: Student; id: 0x1c920ba0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461435> ; data: <fault>),\n    <Student: 0x1cf7b780> (entity: Student; id: 0x1c9298f0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461436> ; data: <fault>),\n    <Student: 0x1dd3f4f0> (entity: Student; id: 0x1a09a3b0 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461454> ; data: <fault>),\n    <Student: 0x1d9e4850> (entity: Student; id: 0x1cbbe040 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461455> ; data: <fault>),\n    <Student: 0x1cf6c000> (entity: Student; id: 0x1a36fc70 <x-coredata://16CBD0F6-B399-4A9C-BD51-5EC98BD99EFC/Student/p461431> ; data: <fault>)\n)}";
}.

Answer 1

您对Student.course的关系筹码定义中有什么样的删除规则（可能是：“无操作”。我认为应为“无效”）。 悬挂引用无效对象通常在技术上与不正确的设置关系有关。 并且还要确保我将添加此内容：courseB.students。 复制到for循环中。

Answer 2

如果仅发生问题，则在处理更改时重新加载视图时，您可以选择缓存数据并同步读取和写入步骤，和/或仅在稳定状态下刷新视图（因此，迁移方法会发送通知完成）。

如果它也发生在其他状态，则应检查模型中的选项（同步，验证，删除规则），或尝试首先保存迁移的学生，然后删除。

如果仍然无法使用，您可以提供模型和关系的屏幕截图吗？

顺便说一句，为什么要迭代每个用户而不是使用

[courseB addStudents:courseA.students];

？ 当然，仅当您拥有CoreDataGeneratedAccessors于您的情况的CoreDataGeneratedAccessors ：

@interface Course (CoreDataGeneratedAccessors)

- (void)addStudentsObject:(Student *)value;
- (void)removeStudentsObject:(Student *)value;
- (void)addStudents:(NSSet *)value;
- (void)removeStudents:(NSSet *)value;

@end