不允许更改核心数据关系，但最终允许删除 child

Question

我有一个包含两个实体的核心数据模型，'Parent' 和 'Child'。 Parent 与 child 有 to-many 关系，child 与 parent 有 to-one 关系。一旦 parent 已设置，我想防止 child 中的 parent 关系发生更改。但是，应该允许删除 child。

child 的集合Parent 看起来像这样：

- (void)setParent:(Parent *)parent {
   if (self.parent) return;
   [self willChangeValueForKey:@"parent"];
   [self setPrimitiveValue:parent forKey:@"parent"];
   [self didChangeValueForKey:@"parent"];
  }

现在，这会阻止 parent 设置后的更改，但同时，它会阻止删除 child，因为设置 Parent 会被重新访问在删除期间两次将 parent 设置为 nil。

删除时第一次调用setParent，self.isDeleted为真。所以我可以对这种情况做出反应。但是在删除过程中又调用了 setParent ，这次 self.isDeleted 是假的，我不知道如何知道是否有人试图编辑 parent 关系或者是否删除了正在发生。

我正在使用 MagicalRecord 2.30，删除调用如下所示：

[MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext)      {

    [sut MR_inContext:localContext];
    [sut MR_deleteEntityInContext:localContext];
}];

我四处寻找有关删除期间那些 setter 调用的信息，但没有成功。因此，我们将不胜感激。

编辑我将一些 NSLogs 放入我的代码中以记录正在发生的事情。删除实际上适用于这段代码，但我不知道所有这些调用是关于什么的。这是相关代码：

- (BOOL) MR_deleteEntityInContext:(NSManagedObjectContext *)context {
    NSLog(@"|");
    NSLog(@"|");
    NSLog(@"----------------------------------");
    NSLog(@"| ***** starting delete... ***** |");
    NSLog(@"----------------------------------");
    NSLog(@"|");
    NSLog(@"|");
    return [super MR_deleteEntityInContext:context];
}

- (void)setParent:(Parent *)parent {
    NSLog(@"|");
    NSLog(@"--------------------------------------------------------------------------");
    NSLog(@"setParent has been called with parameter <%p>", parent);
    NSLog(@"                          self.parent is: %p", self.parent);
    NSLog(@"self.isDeleted is: %hhd", self.isDeleted);
    NSLog(@"         self.moc: %@", self.managedObjectContext);
    NSLog(@"--------------------------------------------------------------------------");
    NSLog(@"|");
    if (!self.isDeleted && self.parent) return;
    [self willChangeValueForKey:@"parent"];
    [self setPrimitiveValue:parent forKey:@"parent"];
    [self didChangeValueForKey:@"parent"];
}

它产生以下输出：

 ----------------------------------
 | ***** starting delete... ***** |
 ----------------------------------
 |
 |
 |
 --------------------------------------------------------------------------
 setParent has been called with parameter <0x0>
                           self.parent is: 0x6080000a9cc0
 self.isDeleted is: 1
          self.moc: <NSManagedObjectContext: 0x6000001c05a0>
 --------------------------------------------------------------------------
 |
 |
 --------------------------------------------------------------------------
 setParent has been called with parameter <0x0>
                           self.parent is: 0x6080000aa080
 self.isDeleted is: 0
          self.moc: <NSManagedObjectContext: 0x6080001c0a50>
 --------------------------------------------------------------------------
 |
 |
 --------------------------------------------------------------------------
 setParent has been called with parameter <0x0>
                           self.parent is: 0x6080000aa080
 self.isDeleted is: 1
          self.moc: <NSManagedObjectContext: 0x6080001c0a50>
 --------------------------------------------------------------------------
 |

Answer 1

如果 isDeleted 是 true，您可以将 parent 设置为 nil，正如@Avi 所建议的。

Answer 2

这是我的发现。我稍微更改了上面的代码以记录反向关系。

- (void)setParent:(Parent *)parent {
    NSLog(@" ");
    NSLog(@"--------------------------------------------------------------------------");
    NSLog(@"| setParent has been called with parameter <%p>", parent);
    NSLog(@"|                                 self is: %p", self);
    NSLog(@"|                          self.parent is: %p", self.parent);
    NSLog(@"|                parent.children contains: %p", [Parent MR_findFirstInContext:self.managedObjectContext].children.allObjects.firstObject);
    NSLog(@"| self.isDeleted is: %hhd", self.isDeleted);
    NSLog(@" ");
    if (!self.isDeleted && self.parent) return;
    if (self.isDeleted) [self setPrimitiveValue:nil forKey:@"parent"];
    [self willChangeValueForKey:@"parent"];
    [self setPrimitiveValue:parent forKey:@"parent"];
    [self didChangeValueForKey:@"parent"];
    NSLog(@"|- after setting the parent ...");
    NSLog(@"|-                                self is: %p", self);
    NSLog(@"|-                         self.parent is: %p", self.parent);
    NSLog(@"|-               parent.children contains: %p", [Parent MR_findFirstInContext:self.managedObjectContext].children.allObjects.firstObject);
    NSLog(@"--------------------------------------------------------------------------");
}

当我删除子项时，会记录以下内容：

----------------------------------
| ***** starting delete... ***** |
----------------------------------
|
|

--------------------------------------------------------------------------
| setParent has been called with parameter <0x0>
|                                 self is: 0x6000000a79e0
|                          self.parent is: 0x6000000a7a40
|                parent.children contains: 0x6000000a79e0
| self.isDeleted is: 1

|- after setting the parent ...
|-                                self is: 0x6000000a79e0
|-                         self.parent is: 0x0
|-               parent.children contains: 0x6000000a79e0
--------------------------------------------------------------------------

--------------------------------------------------------------------------
| setParent has been called with parameter <0x0>
|                                 self is: 0x6080000a8100
|                          self.parent is: 0x6080000a8160
|                parent.children contains: 0x0
| self.isDeleted is: 0


--------------------------------------------------------------------------
| setParent has been called with parameter <0x0>
|                                 self is: 0x6080000a8100
|                          self.parent is: 0x6080000a8160
|                parent.children contains: 0x0
| self.isDeleted is: 1

|- after setting the parent ...
|-                                self is: 0x6080000a8100
|-                         self.parent is: 0x0
|-               parent.children contains: 0x0
--------------------------------------------------------------------------

因此，在删除过程中第一次和第三次调用 setter 时，isDeleted 为真。但是在 setter 的第二次调用中 isDeleted 是错误的。如果我此时测试反向关系，我会发现它已经被删除了。那个测试对我来说已经足够好了。它允许删除循环通过，同时允许运行如果关系根本没有设置setter

不允许更改核心数据关系，但最终允许删除 child

disallow change to core data relationship, but eventually allow for delete of the child

objective-c

core-data

osx-yosemite

magicalrecord