核心数据关系问题

Question

我有一个非常简单的模型，有两个对象：名称和类别。一个名称可以在许多类别中（这是单向关系）。我正在试图用8个名称创建8个类别。示例代码：

 NSMutableArray *localArray = [NSMutableArray arrayWithObjects: 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g1", @"Name", 
            @"g1", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g2", @"Name", 
            @"g2", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g3", @"Name", 
            @"g3", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g4", @"Name", 
            @"g4", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g5", @"Name", 
            @"g5", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g6", @"Name", 
            @"g6", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g7", @"Name", 
            @"g7", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"g8", @"Name", 
            @"g8", @"Icon", 
            [NSNumber numberWithBool:YES] , @"Male", 
            nil], 
            nil]; 
    NSMutableArray *localArray2 = [NSMutableArray arrayWithObjects: 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test1", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test2", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test3", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test4", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test5", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test6", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test7", @"Name", 
            nil], 
            [NSMutableDictionary dictionaryWithObjectsAndKeys: 
            @"Test8", @"Name", 
            nil], 
            nil]; 

    NSError *error; 
    NSManagedObjectContext *moc = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 
    for(NSMutableDictionary *item in localArray) { 
     NSManagedObject *category = [NSEntityDescription insertNewObjectForEntityForName:@"Category" inManagedObjectContext:managedObjectContext]; 
     [category setValue:[item objectForKey:@"Name"] forKey:@"Name"]; 
     [category setValue:[item objectForKey:@"Icon"] forKey:@"Icon"]; 
     [category setValue:[item objectForKey:@"Male"] forKey:@"Male"]; 
     for(NSMutableDictionary *item2 in localArray2) { 
      NSManagedObject *name = [NSEntityDescription insertNewObjectForEntityForName:@"Name" inManagedObjectContext:managedObjectContext]; 
      [name setValue:[item2 objectForKey:@"Name"] forKey:@"Name"]; 
      [[name mutableSetValueForKey:@"CategoryRelationship"] addObject:category]; 
     } 
    } 
    [moc save:&error]; 

这里还有一个问题 - 我已经检查了8类被保存，64名被保存，但只有8所有名称与任何类别连接。所以，当我在分类查询名称：

[NSPredicate predicateWithFormat:@"CategoryRelationship.@count != 0"] 

...有8个元素，当我查询：

[NSPredicate predicateWithFormat:@"CategoryRelationship.@count = 0"] 

...有56元。

当我使双向关系有效时。这里发生了什么？

Answer 1

首先，你的关系应该是总是是双向的。如果他们不是，那么你将会遇到参照完整性和表现方面的问题，正如你已经看到的那样。